A farmer discovers overnight his sheepdog can talk, so to check it's intelligence, he asks the dog to count his sheep. The dog runs into the field, counts them, and then runs back.
'So,' says the farmer. 'How many sheep were there?'
'40,' replies the dog.
'You're not so clever then!' exclaims the farmer. 'I only bought 39!'
'I know,' says the dog.