Kickback reaction

The following collision of two gliders whose product is a single glider travelling in the opposite direction to one of the original gliders. This is important in the proof of the existence of a universal constructor, and in Bill Gosper's total aperiodic, as well as a number of other constructions.

       .....O..
       ......OO
       .OO..OO.
       O.O.....
       ..O.....