Those who demand that everyone "just ACCEPT that Oswald did it"...

[struggle4progress]

297. It's very hard to see in the second video: I had to watch it with repeated stops

maybe a dozen times before I'd seen enough individual frames to be sure. The first indication of anything happening is a little misty ring moving to the right from the right end of the watermelon. Later, at the left end, a conical trail appears and maintains it's conical shape as it lengthens towards the left away from the watermelon

That initial ring puff is aerosol from the initial contact of the bullet with the rind on the right. The conical trail is the debris field of material from the exit point, trapped by the shock wave of the bullet. The watermelon explodes and shreds from right to left, because the pressure front created from the bullet is first seen at the entry point on the right side and continues to be created along the bullet trajectory as the bullet passes through the melon right to left. The total vector-momentum, of course, must be forward -- that is, to the left -- but the total momentum is the sum of the momenta of all individual bits and pieces, and quite a lot moves backwards towards the source of the bullet off-screen at the right