Near the ending assassins are sent to terminate the Drake's. John intervenes and defends himself against the assassin with a battery operated nail gun. He shoots the assassin without engaging the safety mechanism in the nail gun. However, the nail gun used towards the end is not battery powered but actually a compressed air-powered DeWalt nailer that can be jury-rigged to fire without the contact safety mechanism activated.
When Grace is shown on the sidewalk one extra on the right side starts walking while the camera is already filming her.