Routine Test

Bill and Bob, two ten year olds, were sitting in the waiting room of a pediatric clinic. Bill happened to be crying very loudly.
“Why are you crying?” Bob asked.
“I came here for a blood test,” sobbed Bill.
“So? Are you afraid?”
“No. For the blood test, but mom said they will cut my finger to get the blood.”
As Bob heard this, he immediately began crying profusely.
Astonished, Bill stopped his tears and asked Bob, “And why are you crying now?”
To which Bob replied, “Mom brought me for a urine test!”