An electrician says to his wife: "I'm ohm!" She responds: "Wire you insulate?"
This is a pun. In fact, it's three puns, involving the words "ohm", "wire" and "insulate".
All these things have something to do with electricity, and are the kind of things electricians might be interested in. "Ohm" is a measure of resistance or impedence, which is a technical thing. A "wire" is something that can carry electricity from one place to another. And when you "insulate" something, you cover it with a material like plastic to avoid short-circuits or electric shocks.
But those words don't make any sense in those sentences. However, the sentences do make sense if you replace those words with different words that sound very similar.
"ohm" sounds a little bit like "home" (especially in a London dialect);
"wire" sounds a little bit like "why are";
"insulate" sounds a little bit like "in so late".
So now our dialogue makes sense:
An electrician says to his wife: "I'm home!" She responds: "Why are you in so late?"
Puns like this are often used in jokes, especially children's jokes. They are also used in advertising slogans.
For example, a slogan for Coca-Cola used at the Promenade Concerts -- a popular festival of classical music -- was: "The opening movement". A movement can be part of a longer piece of music, and the first movement can be called the opening movement. But when used with a picture of somebody opening a bottle of Coca-Cola, it can also refer to the movement of the hands used to open the bottle.
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