Having already stuffed a string of anal beads deep inside your rectul cavity. Someone who is popping beads is doing so with their expansive yet tight rectul muscle.
Roger and Steve were engaged in sexual escapades. These escapades invariably led to bead popping in that Steve had stuffed a string of black anal beads deep inside Roger. Roger was able to make each individual bead exit his rectul port using the method of popping beads.