While feeding, "Hydra" extend their body to maximum length and then slowly extend their tentacles. Despite their simple construction, the tentacles of "Hydra" are extraordinarily extensible and can be four to five times the length of the body. Once fully extended, the tentacles are slowly manoeuvred around waiting for contact with a suitable prey animal. Upon contact, nematocysts on the tentacle fire into the prey, and the tentacle itself coils around the prey. Within 30 seconds, most of the remaining tentacles will have already joined in the attack to subdue the struggling prey. Within two minutes, the tentacles will have surrounded the prey and moved it into the opened mouth aperture. Within ten minutes, the prey will have been engulfed within the body cavity, and digestion will have started. "Hydra" are able to stretch their body wall considerably in order to digest prey more than twice their size. After two or three days, the indigestible remains of the prey will be discharged through the mouth aperture via contractions.