Related:

• hiding behind the counter] Okay, don't try anything funny.
  I'm armed to the teeth. -- Apu, once bitten twice shy, "Krusty the Clow...
• Measure twice, cut once.
• Once a philosopher, twice a pervert. -- Voltaire
• Hear twice before you speak once.
• I had amnesia once or twice. -- Steven Wrigh
• Once is an accident, twice is coincidence, thrice is enemy action.
• Press [ENTER] once to quit or twice to save changes.
• Try everything once... Try the fun stuff twice...
• Heating with wood, you get warm twice: Once chopping it, and once stacking it.