Top Left: Normal mating of male (on top) and female crayfish. Top Right: Pseudo-copulation between a new dominant male (on top) and a new subordinate male. Bottom Left: After pseudo-copulation, dominant male is in an elevated posture at left and the subordinate male is in a prone posture; aggression between them is low. Bottom Right: After no pseudo-copulation, dominant male at right has elevated claws and posture, and the body of the killed subordinate male is at left. Credit: Donald H. Edwards