Few animals display their mood via facial expressions as distinctly as cats.

In nature we find not only that which is expedient, but also everything which is not so inexpedient as to endanger the existence of the species.

The fidelity of a dog is a precious gift.

Every man gets a narrower and narrower field of knowledge in which he must be an expert in order to compete with other people. The specialist knows more and more about less and less and finally knows everything about nothing.

...he who has seen the intimate beauty of nature cannot tear himself away from it again. He must become either a poet or a naturalist and, if his eyes are keen and his powers of observation sharp enough, he may well become both.

We do not take humor seriously enough.

A man sufficiently gifted with humor is in small danger of succumbing to flattering delusions about himself, because he cannot help perceiving what a pompous ass he would become if he did.