Paddy buys a chainsaw which guarantees to cut down forty trees in an hour.
Paddy sets to work, but only cuts down twenty trees in the hour.
So Paddy takes it back to the shop and says, “This chainsaw doesn’t cut down forty trees in an hour, I’ve only managed twenty”.
With that the shop owner starts up the chainsaw.
Paddy looks at him and says, “What the fuck is that noise?”