A man arrives at Accident & Emergency with a knife sticking out of his chest and staggers to the nearest doctor:
“Doctor! Please help me!”
“Sorry,” says the doctor. “My shift has just ended.”
“But doctor, you have to help me!”
The doctor suddenly pulls the knife out of the man’s chest and stabs it in his eye:
“Take the lift to the second floor. The ophthalmologist has just started his shift …”