Variation on an Idiom

As the two frogs sat on a lily pad, one commented to the other,

“Time sure is fun when you’re having flies.”

-Mike Ridley

Of course it is also true that...

Time flies when you're having fun.

And viewing these idioms concurrently presents a perfect example of why lexical categorizations should not rely on semantic definitions.

In the first sentence "fun" is an adjective and "flies" is a noun.

In the second sentence "fun" is a noun and "flies" is a verb.

Thanks for the laugh Mike.