The answer to this riddle/joke is Sis Boom Bah.
The answer plays a trick on the cheerleading chant (sis-boom-bah) and the sound a sheep makes (bah).
Want more sheep jokes? Get them on Jokes4Us.com.
Tip! The Guardian shares tips on how to tell jokes like a pro.
Of interest, see a list of lyrics, artists and songs that contain the term "sis boom bah" at Lyrics.net.