I spend a lot of time here helping newbies understand that it simply is not meaningful to talk about motion without any reference what it is that the motion is relative to. Today, I had THE most visceral reminder of that that I think I've ever had. My car's idle has somehow gone to being set way too high and I'm going to get in to the mechanic soon, but meanwhile, I'm very aware of the vigorous running of the engine when I park and before I turn the car off. In the grocery store parking lot I pulled through a space such that my car's front was facing the aisle and the cars on both sides of me had their trunks facing that aisle. I parked and RIGHT as I put the car into park, I was fairly sure, the car next to me started backing out and I was so convince that MY car was moving backwards, due to my having inadvertently put the car in reverse that my stomach lurched and I pressed the brake petal so hard I damned near broke my foot. It was a sheer panic reaction and of course would have been the right thing to do had I actually been moving. But I wasn't(*) * relative to the ground, which is what counted.