Bill and Bob, two children, were sitting outside a 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, they cut my finger.

As Bob heard this, he immediately began crying profusely.

Astonished, Bill stopped his tears and asked Bob, "Why are you crying now?"

To which Bob replied, "I came for a urine test!"