Lobsters Scream in Pain When Boiled
This one is often conflated with the issue of whether or not lobsters feel pain when boiled, which is another matter entirely. Many people report that when they put a live lobster into a pot of boiling water, they hear noises that sound like tiny screams coming from the pot. One person—likely feeling a little guilty about tossing a live lobster into a pot of boiling water—probably told their friends the poor thing was "screaming," and the myth was born.
In reality, this one is easy to debunk. Lobsters have no vocal cords, no organs of any type for audio communication. It's just not possible for them to "scream" in any way we could hear, in any circumstance. The sound you may hear is expanding air bubbles trapped in their shells expanding and finding an avenue of escape from their bodies while they boil.
Lobsters are invertebrates and have a primitive nervous system. Whether or not they feel pain in the way you or I would if we were injured or burned is debatable, and since none of us will ever be a lobster, it's impossible to know whether the sensory response associated with injury in a lobster is anything like what we would call "pain." A number of recent studies indicate they do feel pain, or at least pain in their own way. After all, every animal has some method of registering dangerous stimuli and responding to it in a way the discourages contact with that stimuli again.
If you love lobster but don't relish the notion of dropping them into a boiling pot of water alive, consider putting them in the freezer first, or splitting their brain in half with a well-placed cut before cooking. Chilling them makes them torpid and sedated, and splitting their brain will kill them instantly just before you drop them in the water.