Turtle head poking out can mean two things:
1) To have an extreme urge to defecate, so much so that the feces is already spreading the anus and a portion of it is beginning to stick out. So called because it resembles a
turtle poking its head out of its shell.
2) The portion of a long log of shit that protrudes above the water in a toilet. Since it is above the water, it can be smelled. So called because it resembles a turtle poking its head
out of the water.