Big Brain Jar

Big Brain Jar is an abnormally large brain floating in embalming fluid to prevent decomposition. It is presented as a preserved specimen rather than a living organism, with the liquid suspending it and keeping it from rotting.

Its defining feature is its size and its permanent preservation: the brain remains in embalming fluid, which stops decomposition. Beyond that, no additional function is described in the source material, so it should be treated as a decorative or flavor object rather than something with documented gameplay behavior.