We’re all guilty of it — we like to use phrases and idioms that seem to say one thing, but mean something totally different. For instance, if you catch someone napping, you might say that they’re “catching z’s.” What does that even mean?
As it happens, the phrase is a reference to the sound of snoring. The letter “Z” looks like the motion that one makes when using a hand-saw, which was what people commonly used to cut down trees. The sound of the wood being cut is reminiscent of the sound of snoring, so people used to say that someone who was snoring was “sawing wood,” often accompanying the phrase with a hand motion in the shape of a “Z.”
Eventually the hand motion was eliminated and the phrase simplified to include the “Z,” leading to the phrase we know now — Catching Z’s.