My Son: "Why can Ramone [from Disney's "Cars"] move up and down?"
Me: "Because he has hydraulics"
My Son: "What are hydraulics?"
Me: "They are things you can put in your car to make it move."
I realized the lameness and redundancy of my response the second it left my lips, but as my son seemed satisfied (or, more likely, realized he wouldn't be getting an intelligent answer from me), I left it at that.