Our family invaded our house for the evening - the same night my sister decided to try to make jam for the first time. She's never canned before, but the room is filled with experienced persons who were willing to yell suggestions from the living room to the kitchen.
She cooked the jam, but didn't boil the jars. Correcting advice was yelled, and a pot of water was put on to boil. Jars were put in and the family returned to the conversation.
Suddenly my sister marched into the room gripping a jar with the tongs:
"Look what boiling water does to jars!!!!"
After lots of questions about just what this amateur was using to boil her jars - and a slightly panicked closer inspection by three of the males in the family who all claim science backgrounds - she revealed that it was a defective jar that had come from the factory that way.
Happy (early) Half-Fools Day.