The joke "Timber" is one of the old Deaf-culture jokes.
A timber man in the woods cut a tree one by one. He yelled "timber" each time before the tree fell down. Then he came upon a tree that did not respond to the sound "timber". In desperation, he called a tree doctor to come and inspect. The doctor found that the tree was Deaf. The timberman contemplated what to do and got the idea. He called the Deaf timberman for advice. The Deaf timberman said, "No problem. What you need to do is to fingerspell 'timber'." As he fingerspelled "timber", the tree fell down.
See a joke: Birds on the Telephone Lines