Answer: Sounds like a really sneaky critter! Snails feed at night so it isn't likely you'll catch them in the act unless you go out after dark with a flashlight.
Other possibilities include: Caterpillars may be feasting on your pansies. Look for tell-tail frass (technical term for bug poop) on the stems of the plants or on the soil surface. Or, leafcutter bees (although it's a little late in the season for them). These fellas take notches out of the edges of leaves.
Hope the above helps narrow down your search for the culprits!
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