This is a freeze-frame of Robin Unger's muzzle flash.
Note that the muzzle flash is the visible light of the muzzle blast- the sound of the gunshot. So, they are simultaneous. But notice that no one in that image is reacting to the sound of the blast. There is absolutely no indication, from looking at those figures, that a gunshot has occurred. It is absolutely preposterous to think that such a thing happened. Note that that flash is caused by the propellant gases exiting the firearm BEHIND the bullet. The bullet goes ahead of the gases. The bullet precedes the gases. So, look at that picture again because, theoretically, the bullet is already in Oswald. It has already laid waste to Oswald's inside. Yet, he isn't reacting at all.
And look at the shape of that muzzle flash. It's nothing like the muzzle flash from a Colt Detective Special.
Now look again at the one from Robin Unger: it looks more like a flashlight held close to his body.
Then, we also have an open view in at least one other film which does not show a muzzle flash.
That's the instant of the shot, and there is no muzzle flash. And it's followed by this:
Oswald is starting to cringe there, so you know he's been shot. And you can't tell me that, from that angle, we would not see the muzzle flash. Did I mention that it's a flash?
And that makes this image, totally, utterly fake: