The joke is that technically, the contents of your stomach are identical to vomit.
Can you imagine eating vomit? So much vomit that your stomach is full of it? Well guess what? Your stomach IS full of vomit!
Hooray! Enjoy your trip to the bathroom!
Jeeze I wish my art style left room for clever things written on Amos's paper there. I could have come up with so much.
Here, have a close up of the milk carton from last comic.
Haha! It says "regurgitated"