Have you ever noticed that some of the first and easiest words you learn in any new language are the names of animals? And this is doubly true for children.
Now why is that?
Because most of us are especially interested in animals. They fascinate us. (That's why most of what you find on the Internet seems to be cat pictures, for one example).
What interests us, we learn quickly.
Moreover, animals specifically attract our eye. When we have an easy mental image to associate with the word, we learn it faster.
And, unlike many other things that are interesting and highly visual, animals also move. Motion naturally attracts our attention.
This is a principle we can use in all our learning.