A praire dog is when you are taking a shit and your shit doesnt come out all the way and pops back into your ass. Similar to how a praire dog pops in and out of its holes.
The Praire dog is the poop, and your ass is the hole
Alajandro- Hey man! What's taking you so long in the bathroom?
Harold- I just had a praire dog and can't get this last piece of shit out!