There's this joke :

A consultant turns up one day at a farm, and then asks the farmer "if I tell you how many sheep you have, can I have one?". The farmer thinks there's no way he can tell that, so he says "okay". The consultant marshals his forces, studies plans and graphs and pictures, and then tells the farmer "you have 4,760 sheep".

The farmer says that's correct, so the consultant leaves. The farmer catches up with him as he's trying to load his prize into the car. He then says "if I tell you what your job is, can I have it back?". The consultant thinks there's no way a simple farmer can tell what his job is, so he says "ok, go ahead." The farmer then says "you're a consultant."

The consultant is surprised and asked "how did you know that?" so the farmer says "you came up here uninvited, told me something I already knew, and charged me for it. Can I have my dog back now?"