Bed Trap
A husband suspects his wife is having an affair. He needs to go on a business trip for several days, so he decides to set a trap for her. He puts a glass of milk under the bed. From the bed strings, he suspends a spoon over the glass of milk. He has it calibrated so that her weight on the bed will not drop the spoon into the milk. But, if there is any more weight than that, the spoon will drop into the milk and he will detect it upon his return home.
He comes home several days later. The first thing he does is to reach under the bed and retrieve the glass.
The glass is full of butter….
(That must have been one hell of a churning action!)