Learning Medicines

At school little Johnny's class is learning about medicines.

Sister Catherine, the teacher, asks the pupils what kind of medicines they know and what they are used for.

The first pupil said, 'Tylenol?"
"Very good! And what is it used for?"
"It is used for a headache."

The second pupil said, "Nytol."
''Excellent!" said Sister Catherine. "And what it is used for?"
"To help you sleep", replied the student.

Now it is Johnny's turn and he said, "Viagra."
"And what is it used for, Johnny?" asked the surprised Sister Catherine.
"It is used for diarrhea."
"And who told you this, Johnny?''
"Nobody, but every evening my mother tells my father, Take a Viagra, and maybe that shit will get harder."