It was the first day at the sewage works for the young lad, and his supervisor was giving him a tour of duty showing him what was what.

They came to the part of the plant that dealt with solids. The gaffer picks up a turd (he was wearing gloves) and says to the young lad "this one came from the local seamstress - you can see traces of cotton in the motion".

They moved on. The gaffer picks up another turd and says "this one came from the local smithy - there are bits of iron clearly shown in the motion".

Yet another example was demonstrated as coming from the local chippy, as there were wood shavings in the motion.

With that the young lad (also wearing gloves) picked up another turd and tries to guess who had dropped this one into the system, but he can't see any incriminating evidence. So he asks the gaffer.

"That one came from the local homosexual" was the reply.

Inspecting the motion again the young lad was no better off, so he asks the gaffer how he reached that conclusion.

"It's easy lad - can't you see it is countersunk at the bottom?".