Here's something which maybe many of you will have already heard. I read it in the excellent "the Curious Incident of a Dog in the Nighttime". It's maybe something which goes down better in a Pub, but we'll try it here anyway.

Theoretical gameshow.

The contestant is asked to choose between one of three doors.

Behind one is the prize beyond all wildest dreams, behind the other two are gnarly old goats.

The contestant chooses a door but is not allowed to open it. Instead the host opens a different door revealing a goat. The host then asks the contestant if they want to change their choice of door.

What should the contestant do? (assuming they don't have a goat fetish)