At school, Johnny's class is learning about medicines. Catherine, the teacher, asks the students what kind of medicines they know and what they are used for.
The first pupil said, "Paracetamol ?"
"Very good! And what is it used for?"
"It is used for a headache."
The second pupil said, "Restyl."
"Excellent!" said 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 Catherine.
"It is used for diarrhoea."
"And who told you this, Johnny?"
"Nobody, but most evenings my mother tells my father... 'Take a viagra, and maybe that shit will get harder.'"