Maybe one of 'em, anyway. Two-and-a-half words: "That's interesting." If you don't find yourself saying/thinking that TO yourself every day or two, your gray matter is in danger of terminal decrepitation and brain-eating zombies. Alternative phraseology: Well whuduya know; I should know THAT--all connote much the same. Intellectual surprise. Mental epiphany. I hit upon the "That's-interesting" idea a couple of weeks ago and I thought (you guessed it), "That's interesting." Wonderfully self-referential.
It happened when I was pondering why advertising logos were so abstract as to become meaningless, while actually looking at one--I think the Nike "swoosh"--WHEN ALL OF A SUDDEN a Saturn automobile ad came on. I had noticed one or two of these emblems in person in our parking lot but dismissed it visually as pretty curves and circles but symbolically null. When viewed more consciously on the TV screen, however, there it was: THE PLANET SATURN--jazzed up, elided, and stylized ... but Saturn. And I thought ... you know. Paying closer attention would have given me that little intellectual reward much earlier, of course, and I know you are aware of even better examples of what I'm talking about.
Anyway, a couple of things are going on here: our neurons delight in the mind-JOLT, keeping them healthy and long-lived, but also important is a happy mind-SET--a willingness to be continuously SURPRISED by the world. Its complexity and plenitude. And that's interesting.