When certain infected marine mammals (such as whales or sea lions) defecate into the sea, eggs are released and become infected with Anisakiasis larvae while in the water. These larvae are ingested by crustaceans, which are then eaten by fish or squid. When humans eat raw or under-cooked infected fish or squid, they ingest nematode larvae. Once inside the human body, the larvae can invade the gastrointestinal tract. Eventually, the parasite dies and produces an inflamed mass in the esophagus, stomach, or intestine. Some people experience a tingling sensation after or while eating raw or under-cooked fish or squid. This is actually the worm moving in the mouth or throat. These people can often extract the worm manually from their mouth or cough up the worm and prevent infection. Also, some people experience vomiting as a symptom and this can often expel the worm from the body.