1st year students of M.B.B.S were attending their 1st practical class.

They all gathered around the surgery table with a real dead dog.
The Professor put his finger in dog's ass & tasted it in his own mouth.
Then he told them to do the same...
The students hesitated for several Minutes,
but eventually everyone inserted their finger
in the dog's ass & tasted it.

When everyone finished, the professor looked at them & said :
" The most important thing is " OBSERVATION "
I inserted my middle finger
but tasted the index finger !

Now learn to " PAY ATTENTION " :)