Unable to kill enemies using Shadow Strike

[monitor]

Sometimes on the top left of the screen, it says kill 3 enemies using Shadow Strike. I tried to do that but it did not work even I attempted five consecutive strikes on the same individual. It was like I picked up an orc, hit him and he dropped to the floor and repeat. I am at Level 60. Can anybody please explain how it works?

[Pandora]

LT aim a random grunt. X key to shadow strike him.
3 times on DIFFERENT grunts.

You can also stop caring about those silly sub objectives, at this lvl you dont need their reward.

[hotmatrixx]

Originally posted by monitor:

Sometimes on the top left of the screen, it says kill 3 enemies using Shadow Strike. I tried to do that but it did not work even I attempted five consecutive strikes on the same individual. It was like I picked up an orc, hit him and he dropped to the floor and repeat. I am at Level 60. Can anybody please explain how it works?

Grunts, not Captains.