Why does getting your fingers wet help in opening the plastic fruit and vegetable bags from the roll at the grocery store. It seems like wetting them makes your fingers stick to the bag yet, water normally makes things more slippery.
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The evolutionary purpose of fingerprints is not to help catch criminals. They serve to increase friction when the fingertips are wet. Water makes smooth things slippery, but fingerprints evolved to counteract this specific property of water.
Why did I not know this sooner? My wife enjoys watching me struggle to open the plastic bags that come from rolls in the produce department. She can instantly open them with two fingers, the moment she gets impatient waiting for me to open it.
Water is very good at sticking to things, like a plastic bag or a finger. It also washes off the layer of grease on your fingers (generated by your body), decreasing their slipperiness.
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