Then there is the series of jokes where the second part is sort of a spoonerism of the first( the second part is usually left unstated for the listener to spooner, or if stated usually in a less obvious paraphrase)
i.e. "whats the difference between a magic wand and a policemans truncheon(nightstick)??
One is used for Cunning Stunts......
"whats the difference between a nun and a woman in the bath?
" one has a soul full of hope...."
Or " whats the difference between a barrow boy (street trader)and a dachshund
"one bawls out his wares oon the pavement....