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The snail then has choices : it may repair it , replace it with a new one , add an additional one , or go into a period of activity . A strange phenomenon is that many snails return to the same daytime hiding place after each night 's search for food . This ' breathing ' is not so regular or so frequent as in a vertebrate ; moreover , it may cease altogether in the winter when the snail hibernates . The snail moves his direction as well as his head and tentacles to get out of a beam of light . From the evidence it appears the snail fell from a tree and hitting the rock was broken into many pieces . The mandible , the tiny inner ear bones , and sometimes the hyoid ( which supports the tongue ) form the only movable parts of most mammal skulls . This ability of self-fertilization is a very significant feature , because it enables the snail to establish a new colony by means of a single individual . This is essentially a ' toothed tongue . It also normally accommodates the breathing surfaces , in the form of ' gills ' for the operculates or a ' lung ' surface for the pulmonates . Since the keys are based on adult characters , how can you determine if your specimen is an adult ?