Thallspring's botanical chemistry didn't produce the kind of proteins people or animals from Earth could digest.

Such plant material includes much cellulose, and no higher animal can digest this directly.

Usually, such animals cannot chew or digest meat.

And the largest animals do not digest their food terribly well, so that they excrete a great deal.

Humans and many other animals do not digest cellulose.

Further note that the animals cannot digest plants when they are cold.

There is, after all, one thing every animal can digest, and that is its own flesh.

"You can list everything that's in a can of food and that still won't tell the consumer anything about what the animal will actually digest."

Most strains of E. coli do not cause disease, but instead help animals get vitamins and digest food.

Almost no animal can digest cellulose by itself.