As Karl and Danny face the Hoods, Karl tels the Hoods to look at their chests so they can see the infra-red lights from the scopes. Infra-red scopes don't work that way (you do see a red dot but only through the scope and not on the target) but laser sights do mark their targets that way.
When Drummond shoots Kara he uses a silenced, semi-automatic pistol. He fires three times. There is no recoil and the slide never cycles. If the slide remains stationary the spent casing can't eject, a new round can't be chambered, and the pistol can't fire more than once.
There is no evidence that the yo-yo was used as a weapon by Filipinos. It's a myth.