He's comparing the "physical experience" of the ride to hitting a wall --- which is exactly what it felt like the first time I experienced it with my 4-year-old daughter at the wheel, merrily flipping the wheel as far as she could to the right until we smashed into the guard bar, and then to the left, and then to the right again down the entire length of the track, with some random, hard braking (more precisely, abrupt lifting off of the gas) thrown in just to make sure that the whiplash I was experiencing covered the whole 360 degrees. By the time we were done, not a single bone in my body remained in alignment.