Answer:
I am needed for most animals and hardcover books
What is easy to spot but hard to find?
I can be swallowed, but I can also swallow you. What am I?
A hundred arms, a thousand fingers, but I have no eyes to see where I linger. What am I?
You may enter, but you may not come in. I have space, but no room, I have keys, but open no lock. What am I?
What is always coming but never arrives?