Male "Chasmagnathus granulatus" crabs exhibit a "defensive response" to electric shocks. During a study on the ability of shore crabs ("Carcinus maenas") learning to avoid an electrical shock, it was observed that many crabs emerged from the dark shelter to avoid the shock thus entering a brightly light area which would normally be avoided. Immediately after the injection of formalin (an irritant in mammals) or saline into one cheliped (the leg which ends with the claw), shore crabs move quickly into the corner of the aquarium and "freeze" after 2 to 3 seconds. After 1 to 3 minutes, these injected animals are fidgety and exhibit a wide range of movements such as flexion, extension, shaking or rubbing the affected claw. Formalin-treated animals show 20-times more rubbing behaviour during the first minute after injection than saline-treated crabs. Intense rubbing of the claw results in autotomy (shedding) in 20% of animals of the formalin-treated group whereas saline-injected crabs do not autotomise the injected cheliped. During the 10 minutes after injection, crabs in the formalin-treated group tried to use the intact cheliped, guarding the damaged cheliped. The scientists conducting this study commented "the present results obtained in crabs may be indicative of pain experience rather than relating to a simple nociceptive reflex". Other species of crab have been shown to autotomise legs when placed on a hot plate or exposed to a small electric shock. When the antennae of rockpool prawns ("Palaemon elegans") are rubbed with sodium hydroxide or acetic acid (both are irritants), the animals show increased grooming and rubbing of the afflicted area against the side of the tank. Furthermore, this reaction is inhibited by a local anaesthetic, even though control prawns treated with only anaesthetic did not show reduced activity. Other scientists suggested the rubbing may reflect an attempt to clean the affected area as application of anaesthetic alone caused an increase in grooming. In one study, no behavioural or neural changes in three different crustacean species (red swamp crayfish ("Procambarus clarkii"), white shrimp ("Litopenaeus setiferus") and "Palaemonetes" sp.) were observed in response to noxious acids or bases. Shore crabs quickly (within 1 or 2 trials) learn to avoid one of two dark shelters if choosing that shelter consistently results in them receiving an electric shock.