Use your knife to kill two cougars. Do some damage with a gun and then dismount for the final kill using a knife. Stabbing them comes down to timing. They can be tricky; especially if they are coming at you. Once you kill one, watch your back for another.Info on all Ambient Challenges
I think I got this one from a random occurance where a ped was being chased by cougars. So they weren't really paying attention to me.