If you can't bite, don't show your teeth.

Related:

• If you can't bite,
  don't show your teeth...
• If you want your dreams to come true, don't sleep.
  Yiddish...
• You can open a cucumber using only your teeth. --
  Cucumbers are...
• A snake deserves no pity.
  Yiddish...
• Truth is the safest lie.
  Yiddish...
• Trying to define yourself is like trying to bite your own teeth.
  Alan...
• The only advantage of old age is that you can sing
  while you brush your teeth...