Some words might come easily

some words might come easily, for non English speaker there is like a missing context in order to understand, can you explain what is come easily when it refer to words and memory?

And, I also want to test you now. I now will show you 15 words, you'll have 20 seconds to memorize them. Please try as hard as you can as if it would be an exam. And after those 20 seconds, we will see. Time starts now. Try as hard as you can. You still have 10 seconds. Look at all the words, however you want. Five seconds. Three. And ... Time is over. Now see how much you can remember. Really try to find all of the words in your head. Go from one to the other. And what I can tell you is that some words might come easily, some might take some time, and some might not come at all.