Monkey See, Monkey Doom 15
In Diner Turned, retrieve a chained Cymbal Monkey in a Public Match.
After killing a bunch of zombies consecutavly, a symbol monkey will randomly drop. You need to grab it and throw it at a small group of zombies (more then 1). It will chain them together and kill them. Once they die, another white monkey (white glowing) will spawn, pick it up and the achievement will pop.