Doctor, I fell on my elbow.

'Alright, I’m going to prescribe you a cream. Apply it exactly where you fell. Come back in three days.'

Three days later, the man returns with a massively swollen elbow.

'Did you do what I told you? Did you apply the cream where you fell?'

'Yes… I was very precise.'

'Good. So what happened?'

'Well… I’m lucky I remembered the exact spot on the floor in front of my bathroom door.'