The monkeys can change your power-up into a perk. The perk bottle shows up for less time than the power-ups. When you're that close to the monkey it can be tough to see what exactly they have. I have seen the bottle when the power-ups are cycling through, but I can never seem to get it. According to other players, the perks obtained from the monkeys can never be lost. Even if you're downed or die and respawn after your partners finish the round. How awesome is that?!