if its isolated to random leaves here and there... and you dont see any caterpillar turds anywhere, its probably leaf cutting wasps or some other flying insect.
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no clue what sort of wasps do this, but i know its done to my plants occasionally..
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small caterpillars seem to leave the veins of the leaves intact. thats a clue right there for teeny tiny caterpillars.
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the turds are the best give away though.