Pun with "effervescent" and "fiddlesticks"
I read a pun in a children's joke book "Effervescent enough covers on your bed, your fiddlestick out." I know that "fiddlestick out" is "feet will stick out", but what is the "effervescent" punning on?
Effervescent=If there isn't.
Which should be: if there aren't.