Urine test

Two children are in a doctor's waiting room, and one of them is crying.
"Why are you crying?" asked the other child.
"I'm here for a blood test, and they're going to cut my finger."
When he heard this, the other child started to cry.
"Why are you crying?"
"I'm here for a urine test."

from http://www.jokes2go.com/jokes/24780.html?19