It's not only the lapel flip, his whole right shoulder snaps forward as the bullet rips through him. Look again.
I am still waiting for NBC to release the last half of their Original Darnell Film. That will give us clearer images of the railroad yard, and that area leading into the Elm St Ext from the railroad yard. We will also glimpse down into that space between the Zapruder Perch and the N-S Picket Fence. There are extremely few images of this area which showed Black Dog Man on Willis 5.
What's really fascinating is that the bullet that your assassin fired not only missed Jackie and didn't damage the interior of the limo, but destroyed only the right side of JFK's brain!
You're description requires an Exploding Bullet.
Way back when, there was a TV Commercial with the tag line, "It's not nice to Fool mother nature". Please bear this in mind when you decide to Cease displaying Gov Connally's movements at that exact point in time on the Zapruder Film. Not cool.