Why does my cat's ......?

bacteria could be building up in his digestive tract. feed him hard food, cats who eat soft canned food often have more gas. try switching his food. or maybe giving him a teaspoon of plain yogurt to promote the growth of healthy bacteria. i've also heard that animals can be so into thier emotions they have a physical reaction - such as farting when excited or startled. so don't diss the gas, honor the fart.