system
Given the following post, respond as if you're commenting on Reddit:
human
[Godzilla 2014] (Spoilers inside)

So we learn in the movie that M.U.T.O. and Godzilla used to live off radioactivity (there is some part in the movie where they say the reason Godzilla goes to live underwater is to absorb the earth's core radiation). **My question is, how come these monsters have a mouth?** It makes no sense from an evolutionary point of view that these monsters have a working, ingesting mouth. It would make sense to have teeth and other dangerous parts to defend from predators, but M.U.T.O. ingesting radioactive barrels? Why are they grown with working mouths?
gpt
I don't think they only feed of radiations, they still need matter and nutriments to grow.
Radiations allow them to grow fast and big. Instead of only using combustion for their metabolism, they must have found a way to also fuel it via radiation.