Sheldon Allan Silverstein - Warning

Inside everybody's nose
There lives a shar-toothed snail.
So if youi stick your finger in,
He may bite off your nail.
Stick it farther up inside,
And he may bite your ring off.
Stick it all the way, and he
May bite the whole darn thing off!

Sheldon Allan Silverstein

http://www.poemhunter.com/poem/warning-27/