Predatory snails generally have two ways of getting into a shell. Some drill a nice round hole and insert the proboscis into the victim and ingest the soft tissues, but this is very time consuming, taking hours or even days to complete. The second method is to enter the victim's shell through an existing opening, such as the aperture of a snail or the space between the two valves of a clam, but the victim may react violently by closing the aperture with the operculum or clamping the valves together. If the predator has already gained entrance the proboscis can even be severed, but if part of the shell can be wedged into the opening this will stop the closing. It turns out that a small tooth on the edge of the outer lip of the predator's shell is an effective tool to keep the opening from being closed. Obviously it is a trick worth developing.
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