He answered, "A particle accelerator."
We both were like WOW! Huh... you want a grilled cheese sandwich with that?
His school is a science focus school, so he has extra science very Tuesday afternoon and Lego classes every Thursday afternoon, extra work and time at school; but he really loves it. They also had a book fair that included some books at his reading level plus a little that's all on physics and the periodic table. He's been reading them and finds that his favorite character is "inertia".
Probably because in Mythbusters there was an episode that included the plausibility of the Knightride scenerio of driving KITT onto a moving truck while driving at speed. The Mythbusters figured out that the car's inertia kept it from accelerating madly when it hit the ramp... it simply tends to go the speed it was going, even if the truck is doing all the work. But Jet really remembered that Inertia was KEY.
We also had the most interesting discussion of Schrödinger's Cat I've ever had with an eight-year-old. All right, that I've ever had with anyone outside of Caltech. *laughs* Chem 1 started with Schrödinger's Equation.