A Fly and a Flea

A fly and a flea in a flue
Were imprisoned, so what could they do?
Said the fly, "Let us flee!"
"Let us fly!", said the flea.
So they flew through a flaw in the flue.

Heard during MUET Listening

(Source: http://www.odps.org/glossword/index.php?a=term&d=11&t=51)