Byrne & Russon argue that the action and program levels of imitation form two discrete categories, with no intermediate steps. A Piagetian view enlarges our understanding of human and ape imitation by showing the developmental paths that imitation takes in the sensory-motor period of intelligence. It is clear from Piaget's (1945/1962) analysis that the action level of imitation is richly varied and that intermediate steps do occur between the action and program levels.