Ass Reflex
Is similar to the case known as "Acid Reflex" except only affects the rectal region. Also refer to "Shart" or "Mud Butt". It's not quite a fart, but not quite a shit either. A warm and excessively moist passing of gass/poop liquid.
After eating Chow Mein at Coleton's Shit Shack, I had contracted a bad case of Ass Reflex. The sensation was quite unpleasant, smelly, warm, and even spicy!