Hi, I have them on paper towel, so no substrate. I just got them home and noticed. Whe we were at the expo, my father did notice that they were kind of agressive and doing it really hard. Ofcorse I did not check the snake until I got home. The snake did take a poop and it was really like pasty I guess I could say like it was scattered on the paper and still had hair in the poop... Anyways back to the vent, it's just really red/swollen and almost open looking not like hanging open but just a tad open I guess I could say lol, I ended up buying 2 snakes off them which both have the same problem.