a pillow is shaped to encourage a sleeper to sleep on a side , rather than on the back . this is accomplished by providing a pair of arms extending forwardly from a head support . the arms are spaced apart less than the width of the sleeper &# 39 ; s shoulders so it is uncomfortable for the sleeper to roll over onto the back . the arms are spaced from the edges of the pillow to provide for a side ramp , inclined upwardly toward the head support , to receive the forearm of the sleeper .