A computer programmer has been missing from work for over a week.
Finally someone notices and calls the police.
They break down the door of his flat where they find him dead in the shower, an empty bottle of shampoo next to his body.
The programmer seems to have died from a combination of exposure and exhaustion.
The puzzle is explained when the police read the instructions on the shampoo bottle – ‘Wet hair.
Apply shampoo. Rinse. Repeat.’
This joke is included in the Black Book of Jokes. You can order it from here.