Watch the following video while thinking either the term "green needle" or "brainstorm."
Now do it again. And again. And again, this time while picking your jaw off the floor.
The video, which was first posted on Reddit, is an example of "priming," according to an old psych professor I happen to have on speed dial. Priming is a psychological concept in which one stimulus influences a response to a subsequent stimulus. Here's an example, from the book Thinking Fast and Slow by Nobel laureate Daniel Kahneman: If I ask you what you had for lunch and then, immediately, ask you to complete the word fragment SO_P, you are likely to say "soup." If I ask you when you last bathed and then asked you to complete the same fragment, you're more likely to to say "soap."
Our brains are constantly making associations, whether we're aware of it or not. Sometimes this can be harmful (stereotypes are also a form of priming), but sometimes, as with this video, it can seem like magic.