ALAN TYANI
That depends, that varies from one person to another.  You can just open the door ajar and throw the grenade without checking whether the people were there or not.  You can open the door fully trying to locate your enemy as a trained man before hitting at the enemy.  That condition varies from one person to another.  I also have a belief that if it was bright he couldn't have looked through to see what was happening at the passage.