I don't understand why anyone would use a knife period. It's just dumb. I have seen it done and it's doable, but it's just an unnecessary risk when you can just put another one in the chest.
On my way out of Africa I was asked to help a local farmer cull a diseased giraffe the morning I was flying out. Wasn't going to turn down a free morning of hunting and we went out and located the animal. We put the animal down, but he was still alive upon approach. I went muzzle to skin on the head where the PH advised. Obviously, I didn't hit the brain and the bull went from lifeless to full on standing, thrashing, bucking in an instant while I was standing almost arms reach away. Could have ended badly for sure, I got lucky. Let's just say it was quite the scene when that happened and the biologist who wanted to study the animal probably wondered what the hell we did to the poor thing when he saw how many holes were in it.