Multimedia 1. The terrestrial hermit crab, Coenobita compressus, produces chirping sounds and vibrations during a shell contest. Here, the aggressor crab (occupying a Clypeolum latissimum shell) runs at the defending crab (occupying a Pomacea sp. shell). A chirping/croaking sound is heard at 2s onwards as the aggressor mounts the defenders shell and begins to examine it.