Yael: You must be a having a good day. The smile on your face is a mile wide.

Don: I'm finally going to get revenge on my neighbor.

Y: For what?

D: He has the loudest lawnmower you've ever heard. And as if that isn't enough, he mows his lawn every Saturday at seven a.m., like clockwork, and wakes me up on the one day I can really sleep in!

Y: So what are you going to do?

D: It cost me three-hundred bucks, but now my lawnmower is even louder than his. And starting this Saturday, I'm going to set my alarm for six a.m. every weekend so I can beat him to the punch and wake him up with my lawnmower before he can wake me up with his!

Y: It sounds like your revenge is costing you a heck of a lot of money, what remains of your hearing, and a good deal of sleep to boot.

D: And it's worth the price!

Y: It costs you more money and sleep for your revenge than it did just to listen to his lawnmower. As irrational as this is, however, it's also normal human behavior. A study confirms that thoughts of revenge can be so pleasurable that many of us are willing to pay extra for it. PET scans of the brains of people contemplating revenge showed a positive correlation between the amount of activity in reward-related areas of the brain and how much a person was willing to pay for the revenge. It just goes to show how our passions can interfere with rational behavior.

D: Man, thinking about revenge is seriously sweet. Did I say six o'clock? On second thought, how about four?