Something simply pearl-fect about these teeth, and a neat simile to describe the darting in and out of an endlessly worked toothpick. 

… the seed-pearl teeth, where a tooth-pick ran ceaselessly in and out, in and back again, like a mouse in a cage. 

Source: Louis Golding, Good-bye to Ithaca (London: Hutchinson, 1955), p. 48