Kill 7 monkeys in under 10 seconds in the Rebirth labs.
The mission the monkeys are found on is named "Rebirth". The monkeys are found once Hudson starts talking to you. You will hear loud screeching and find monkeys in cages on the walls stacked on top of one another. Before you enter the big circular room, you will see a corner that is full of cages on your right. Directly before this hallway on the right side, is a AK-74u with a grenade launcher attachment (the room has pigs inside it). Grab the AK-74u and equip the grenade launcher attachment with . Back away from where the monkeys are at and aim so that the grenade will hit the floor. This should kill all the monkeys in the corner.
If you dont use the grenade for this one then another way to do it is when you enter the big room go all the way to the door and one of the guys has a gun with a red dot sight on it. It can be fired on semi and you can acurately take all of the monkeys out that are right in front of the big room one at a time in way less then 10 seconds.