“Oh Bob,” sighed his wife. “I wish you wouldn’t go down the pub every night. You drink far too much. Here, let me show you something.”

Bob’s wife put two glasses before him, one filled with whisky, the other with water. Into each she dropped a worm.

The worm in the water swam around happily while the worm in the whisky had a fit and sank to the bottom, dead.

“There!” said the wife triumphantly. “Now what does that show you?”

Bob looked at the two glasses and replied, “It shows me that if you drink, you won’t get worms. Now I’m off to the pub.”