Back in the 18th century, French sailors wore hats with pom-poms to protect their heads from bumping on low deck ceilings
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What is usage of the square hole in the Chupa Chups stick
It's not to save a child from choking, as many believe: that's what the empty length of the stick is for. The side hole is made to keep the candy on the holder.
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What is the hole between the camera lens and flash on iPhones?
An auxiliary microphone. It makes the sound on recordings clearer, helps Siri understand accents, and reduces the noise captured by the main mic.