A dog goes to a telegraph office and dictates a message.
‘Woof, woof, woof, woof, woof, woof, woof, woof, woof.’
The operator reads it back then says, ‘You know, we charge per ten words, so if you want you could have an extra ‘woof’ for free.’
‘No thanks,’ says the dog.
This joke is included in the Black Book of Jokes. You can order it from here.