is it a proverb ?

Is this sentence a proverb:
"Don't eat yellow snow "

What does it mean ?

You are joking, right? I always thought it meant for kids not to eat snow where a dog had obviously urinated. My parents never had to tell me this, but I think a lot of parents do say this-maybe as a joke.

It's from the lyrics of a Frank Zappa song - Don't Eat The Yellow Snow. See the full lyric here:

http://www.seeklyrics.com/lyrics/Frank-Zappa/Don-t-Eat-The-Yellow-Snow.html

Always (almost always?) said as a joke.