FBI Agent,
What do you call a foreign object in a chip pan?
a foreign object = an unknown object that doesn't belong in the pan
chip pan = a frying pan used to deep-fry chips
chip = rectangular piece of fried potato
Answer: UFO, unidentified frying object
UFO = Unidentified Flying Object, sometimes called a flying saucer. This is the normal meaning of the abbreviation UFO.
This joke is an example of a pun. It is funny because "frying" sounds almost like "flying".
From the Oxford English Dictionary
pun - noun
The use of a word in such a way as to suggest two or more meanings or different associations, Or THE USE OF TWO OR MORE WORDS OF THE SAME OR NEARLY THE SAME SOUND WITH DIFFERENT MEANNGS, so as to produce a humorous effect; a play on words.