Cats may experience gastrointestinal problems after eating crab, especially kittens with weaker constitutions, who may experience issues about an hour after consuming it. Therefore, it is not recommended to feed crab to kittens, primarily due to the crab's structure, which can easily cause indigestion or even intestinal obstruction. If you discover your cat has eaten crab, seek veterinary attention immediately. 
Besides crabs, what other foods can't cats eat?
1. Onions and garlic. Onions, garlic, shallots, and scallions can damage a cat's red blood cells, causing anemia. Cats will definitely be poisoned if they eat large amounts of these foods, but they will also be poisoned if they eat onion soup or garlic powder, which are made from concentrated onions or garlic.
2. Milk. Cats cannot digest the lactose in milk, which may cause them stomach upset or diarrhea.
3. Raw eggs, raw meat, and bones. Just like humans, cats can become infected with Salmonella or E. coli if they eat raw eggs or raw meat. Symptoms vary and may include vomiting, diarrhea, and lethargy.
