The shadow on the wall.
Silent
In BTB exclusively you get points depending on the style of kill. EG: If you killed him with a headshot, it would count for two points, but if it was a vehicle it would only count for one.
I had to do a double take and a few tests the first time I saw it, but you figure out which weapons do what.
You can also download the gametype and go into the scoring options to check what you get extra points for.