This seems like a no-brainer. Jumping, leaping, or otherwise attempting to get on a moving vehicle of any sort is dangerous. Here it is phonetically... Dane-ger-us. I think however, that if the vehicle in question was this particular wagon you may be okay. After all, it is being pulled by two dogs and is loaded down by lots of pipe smoking peasant-type people. So I imagine it's moving just a hair faster than you or I would walk.