Firstly, the organism doesn't need to eat or breathe because it can harness cold fusion in its cells, they split water molecules and merge the two hydrogen atoms together to make helium and lots of energy.
Secondly, Dr Blair believed it has a default form and was likely artificially created to spread an alien civilization around the universe. When they found the creature it had three red eyes and tendrils in its head and Dr Blair came to the conclusion that when it had finish assimilating all the life forms it would return to its default form, unless it needed adaptations to survive.
Thirdly, the creature is telepathic and as it thawed out in the book, it would mess with the minds of the crew and it knew what they were all going to do. They couldn't hide anything from it.
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