What do you call this?

Searching for a literary term . . . something more specific than "catch-phrase" – this is something my mother and father both said, which I think they picked up in Oklahoma and/or Idaho in the twenties:

When someone made an inadvertent rhyme in conversation, my mother or dad would always say "He's a poet and don't know it, but his feet show it:  They're long, fellow."

Do any of the linguists in the company assembled know what you call an automatic paranomasia like that?

Joe