Brains are mostly fat... so it could be the time for enough heat to transfer into the brain for it to melt and all the neurons short out. Getting too hot is way

Brains are mostly fat... so it could be the time for enough heat to transfer into the brain for it to melt and all the neurons short out. Getting too hot is way more dangerous for your brain than getting too cold. Some brains can also rapidly shut down consciousness in response to overwhelming pain, but I suspect that's not relevant for lobsters... getting their limbs torn off and re-growing them is a thing. If a bigger lobster rips your arm off, you'd better remember where it happened and respect their territory.