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1.
When you need to go to the toilet so badly that the poo is starting to make an appearance from your bum hole.

Usually accompanied by walking around on tippy-toes and gritting your teeth.
Oh man! Where's the nearest restrooms? I've got a curious tortoise!!
by doc brown May 29, 2007
 
2.
A (usually unexpected and unwanted) poop that starts to stick out it's head to check out what's happening, usually as it's owner is running to the bathroom in an attempt to deposit it before it fully merges.
I tried to casually let one go and thought I'd got away with it, but then I felt something poking at the back of my pants. It was like a curious tortoise straining it's head to see the world around it.

I made it to the bathroom just in time and it had a water birth. Now I have to wash my jocks.
by DustyRoads September 27, 2013