We have two kitchens and therefore two refrigerators and we never seem to have mayonnaise in the main kitchen. So, the other day, DH went looking and found five, yes five, opened and partially used jars of mayonnaise. Upon questioning my son, the main suspect, he learned that DS had accidently left a jar of mayonnaise out on the counter overnight and then put it in the fridge in the morning. Not wanting to risk certain death, he opened a new jar rather than use that one. The next time he wanted some, he could not remember which was the bad jar so he got a new one from the pantry...and so on and so on.
So, now we have four good jars and one risky one and no one knows which is which.

Kids!