user151: What is the difference if the snake was eating a frog or a human? What do Buddhist scriptures say about this? 

user8157: Based on the monk's Vinaya (rules), intentionally killing a human being results in immediate expulsion from the monastic community where as killing a snake does not. Therefore, killing an infant is far more serious than killing a snake. 
This is based on the natural laws of kamma known within our heart. If we must kill the snake to save the infant, we should kill the snake because if we allow the snake to kill the infant, we will feel great regret & remorse in our heart &, even worse, other people will blame us for our lack of compassion towards the child. We may be socially ostracised & rejected. 
The snake was murdering the child thus the snake will reap its 'own kamma' (even though, in reality, animals are not subject to the laws of kamma). 
The scriptures (AN 6.63) teach 'kamma is intention' & 'kamma only comes into play due to sense contact'. Therefore, the only repercussions/consequences of killing the snake will be known within your own heart & nowhere else. 

When I lived in Thailand, alone near a village, I walked passed a very large cobra laying across the road to the village. Upon closer inspection, the cobra was fighting with an even larger python and had its jaws wrapped around the python's neck. A monk's house was nearby so I informed the monk, who returned with a big stick and hit the cobra until the cobra detached. We did this to save the cobra's life, since it could easily be crushed by a motor vehicle driving to the village. 

On another occasion, a large cobra was in the visitor's quarters. Again, we had to use a large stick to remove the cobra. Although cobras are our friends, sometimes we must be firm with them. 

user111: Here are 2 stories from the Abhidhamma commentary.

A farmer who, after having taken his precepts from a respected monk,
  went to look for his buffalo that had strayed into the forest. Along
  the way, he was caught by a python. His first thought was to use his
  axe to kill the snake coiled around him. Then he remembered that he
  had taken his precepts from a respected monk. The thought came to him
  for a second time and again he refrained from killing. The third time
  he was prompted to kill, he threw away his axe. The snake uncoiled
  itself and freed him.
A lay devotee who was told by a physician to give rabbit meat to his
  sick mother to get her well. When he caught a rabbit, he thought that
  to take a life so that his mother could prolong hers was wrong. So, he
  freed the rabbit. On reaching home, he was scolded by his elder
  brother. However, he stood by his sick mother’s side and said, “Since
  I was matured enough, I’ve never intentionally taken a life. By the
  power of this truth, may my mother be healed.” This asseveration of
  truth saved his mother’s life.

What is the difference if the snake was eating a frog or a human?
Saving a human is much more meritorious compared to saving a frog
If a snake is eating a human infant in front of me what should I do?
Killing breaks the first precept no matter how you try to justify it!
So, try to save the human without killing the snake. Use wisdom instead of fear/aversion towards the snake.
They say snakes dislike clove, cinnamon smell. Even a pepper spray might work.
If you don't have those, try making loud noises and threatening gestures with sticks & stuff. 

user10479: Just kill the snake and save the baby
Ok , this would be the reaction of a person who has no idea what Buddhism is . But , even if we know Buddhism to some extent, we would do the same . Because still our minds are not developed. 
According to Buddhism 
Basically all lives are equal , if a snake is eating a frog , there will be no reaction from a person who has achieved nirvana. If the snake is eating a human (even if the infant is his own kid , there won't be a difference )he would never kill the snake , he will try to remove the snake using a stick , if it doesn't succeed,he will give himself to the snake and will save the life of his kid or any other human. But if the snake is eating some other animal, he will not interfere . Because according do Buddhism , people should not interfere with animal lives , all those things are unnecessary attachments. Buddha advises not to have pets , not to even give food to animals continuously , because if you do those animals will start to make bonds with you and you with them , that will definitely make ones samsara longer . 
Conclusion
People should not interfere with actions of animals. But you can save any human being by sacrificing yourself or by using some strategy 

151: <p>What is the difference if the snake was eating a frog or a human? What do Buddhist scriptures say about this? </p>
 8157: <p>Based on the monk's Vinaya (rules), intentionally killing a human being results in immediate expulsion from the monastic community where as killing a snake does not. Therefore, killing an infant is far more serious than killing a snake. </p>

<p>This is based on the natural laws of kamma known within our heart. If we must kill the snake to save the infant, we should kill the snake because if we allow the snake to kill the infant, we will feel great regret &amp; remorse in our heart &amp;, even worse, other people will blame us for our lack of compassion towards the child. We may be socially ostracised &amp; rejected. </p>

<p>The snake was murdering the child thus the snake will reap its 'own kamma' (even though, in reality, animals are not subject to the laws of kamma). </p>

<p>The scriptures (AN 6.63) teach 'kamma is intention' &amp; 'kamma only comes into play due to sense contact'. Therefore, the only repercussions/consequences of killing the snake will be known within your own heart &amp; nowhere else. </p>

<hr>

<p>When I lived in Thailand, alone near a village, I walked passed a very large cobra laying across the road to the village. Upon closer inspection, the cobra was fighting with an even larger python and had its jaws wrapped around the python's neck. A monk's house was nearby so I informed the monk, who returned with a big stick and hit the cobra until the cobra detached. We did this to save the cobra's life, since it could easily be crushed by a motor vehicle driving to the village. </p>

<hr>

<p>On another occasion, a large cobra was in the visitor's quarters. Again, we had to use a large stick to remove the cobra. Although cobras are our friends, sometimes we must be firm with them. </p>
 111: <p>Here are 2 stories from the Abhidhamma commentary.</p>

<blockquote>
  <p>A farmer who, after having taken his precepts from a respected monk,
  went to look for his buffalo that had strayed into the forest. Along
  the way, he was caught by a python. His first thought was to use his
  axe to kill the snake coiled around him. Then he remembered that he
  had taken his precepts from a respected monk. The thought came to him
  for a second time and again he refrained from killing. The third time
  he was prompted to kill, he threw away his axe. The snake uncoiled
  itself and freed him.</p>
  
  <p>A lay devotee who was told by a physician to give rabbit meat to his
  sick mother to get her well. When he caught a rabbit, he thought that
  to take a life so that his mother could prolong hers was wrong. So, he
  freed the rabbit. On reaching home, he was scolded by his elder
  brother. However, he stood by his sick mother’s side and said, “Since
  I was matured enough, I’ve never intentionally taken a life. By the
  power of this truth, may my mother be healed.” This asseveration of
  truth saved his mother’s life.</p>
</blockquote>

<p><strong>What is the difference if the snake was eating a frog or a human?</strong></p>

<p>Saving a human is much more meritorious compared to saving a frog</p>

<p><strong>If a snake is eating a human infant in front of me what should I do?</strong></p>

<p>Killing breaks the first precept no matter how you try to justify it!
So, try to save the human without killing the snake. Use wisdom instead of fear/aversion towards the snake.</p>

<p>They say snakes dislike clove, cinnamon smell. Even a pepper spray might work.
If you don't have those, try making loud noises and threatening gestures with sticks &amp; stuff. </p>
 10479: <p><strong>Just kill the snake and save the baby</strong></p>

<p>Ok , this would be the reaction of a person who has no idea what Buddhism is . But , even if we know Buddhism to some extent, we would do the same . Because still our minds are not developed. </p>

<p><strong>According to Buddhism</strong> </p>

<p>Basically all lives are equal , if a snake is eating a frog , there will be no reaction from a person who has achieved nirvana. If the snake is eating a human (even if the infant is his own kid , there won't be a difference )he would never kill the snake , he will try to remove the snake using a stick , if it doesn't succeed,he will give himself to the snake and will save the life of his kid or any other human. But if the snake is eating some other animal, he will not interfere . Because according do Buddhism , people should not interfere with animal lives , all those things are unnecessary attachments. Buddha advises not to have pets , not to even give food to animals continuously , because if you do those animals will start to make bonds with you and you with them , that will definitely make ones samsara longer . </p>

<p><strong>Conclusion</strong></p>

<p>People should not interfere with actions of animals. But you can save any human being by sacrificing yourself or by using some strategy </p>
