“The question is, what is a Mahna Mahna?”
“The question is, who cares?”

The Mahna Mahna song (Piero Umiliani, 1968).

Performed by Mahna Mahna and the Snowths, (The Ed Sullivan Show, 1969). From YouTube.

See also:

song history on Wikipedia,
lyrics on poppyfields.net,
audio (mp3) on latke.net,
video (mpeg) on mahnahmahna.net.