A professor of medical school said to his students on the first day of class: "The most important thing to be a doctor is to be bold and careful!".
He put one finger into the cup of urine and stuff it into his mouth then handed the cup to the students asked if anyone can do it again.
After a short silence, one student stand up and put his finger into the cup then stuff it into his mouth.
The professor smiled slightly said:"Yes, yes, you are bold enough" after while he continued:" but it's a pity that you didn't look carefully enough, no one noticed that I put my index finger into the urine cup and my middle finger into my mouth!"
