I encountered this lightbulb joke today, but I can’t figure out why it is funny:
Q: How many flies does it take to screw in a light bulb?
A: Two, but I don't know how they got in there.
My best guess is that this is a play on the meaning of the word “screw”, suggesting that the flies are flying in circles inside the bulb, but I could not find this meaning in the dictionary.