Here's a joke I once read in a worn volume of rib ticklers. A bit off color, but my ribs loved it.

Question: How does a blind parachutist know when he's approaching ground? Answer: His leash goes slack.

The lines stuck and I soon carried them home to my wife, my very English-capable wife, who taught me anew that humor has a hard time leaping cultures. Somehow the meaning always gets lost and our conversation soon becomes a joke in itself -- one invariably on me.