The mind is a strange thing. I’ll never forget learning about sublimation in school though I couldn’t tell you much else from chemistry class. Our teacher brought a good sized chunk of CO2 as a demonstration. We put some pieces in water and watched the thick fog roll out of the container towards the floor. I even remember the teacher placing a penny on the dry ice and it sounding like it was screaming.
I try to avoid gags about body functions–it’s just not a place I like to go. But in this case it was necessary–if nothing else, I tend to get a chuckle from the kids when I tell this joke.