I wish I could turn down the sound effects volume. Some cool concepts for sure! And then it froze as I was rewinding.
Ah...don't think it was stuck then...
*Spoilers* You are rewinding, going backwards, so when the "flash" pops up you need to re-shoot the enemy you shot when advancing forward (it could be off in the distance or hidden among "arm" sprites depending on when you shot it!). Basically if there is a crosshair on the screen, that means there is something you can shoot!