Did you know that over-eating can be lethal for a squid? It actually has nothing to do with their heart. It would only take a single oversized meal to kill or cause brain injury to a squid. Squid are part of a diverse group of highly evolved invertebrates called cephalopod mollusks. Cephalopods, which also include octopus and cuttlefish, have the largest and most complex brains of all the invertebrates.
Like all invertebrates, squid don't have a bony skeleton. And squid even lack a hard outer shell like many other mollusks have. But squids' brains are protected by a capsule of flexible cartilage. And the squid's digestive system passes right through its brain!
Although the cartilage surrounding the brain is flexible, it doesn't stretch. However, the esophagus running through the middle of the brain does stretch. If a squid tried to swallow too large a piece of food, the esophagus would expand, squashing its brain into the sides of its head.
But squid are well adapted to avoid this problem. They have hard chitinous beaks, sort of like a parrot's beak, that breaks up even hard-shelled food into manageable pieces. The food is further broken down by strong enzymes in their saliva, and a hard, raspy tongue-like structure called a radula. The radula is covered with rows of small sharp teeth specially adapted to grinding and shredding. So the squid's dinners are reduced to tiny particles before swallowing.