This means that, while capable of movement, the animal moves infrequently. When the animal does move it either glides slowly on its base or summersaults. For all practical purposes, the prey animals the Hydra eats must accidentally brush it and trigger the cnidocytes for the prey to be captured by Hydra . Just as Hydra is not an active carnivorous animal, it also senses and responds to it's environment only minimally. The nerve net is connected to sensory cells located among the other cells of the animal.
Hydra is attracted to food, moderate light and moderate temperatures.
It avoids light and temperature extremes and harsh chemicals. It also responds to touch. Once food has been senses, paralyzed by the cnidocytes and ingested into the gvc, digestion of the prey animal begins. This is a two step process. The first step is called extracellular digestion.