third thrust severed the jugular vein, as the blood spurted out in a stream all over me.

Read the tale of the turn of the century game warden form Africa.  The entire story is a nail biter, but the main point is below and after the jump.

CA has a post up about being able to do the deed.

You must be able to complete the act, but you must also be able to keep your head about you and continue to function while in the thick of it.

Either of these alone is good, but combined makes you a force multiplier.

From the Great Hunters via Your Crazy Uncle

What happened next, of course, occupied only a few seconds, but I vividly recall the unpleasant sensation of expecting the crunch of the lion's jaws in my person.

However, the terrified horse was bucking and plunging so violently that the lion was unable to maintain its hold, but it managed to knock me out the saddle. Fortune is apt to act freakishly at all times, and it may seem a strange thing to suggest that it was fortunate for myself that I happen to fall almost on top of the second lion as he was running round in front of my horse, to get hold of it by the head. Had I fallen otherwise, However, it is probable that the lion would have grasped me by the head, and then this would assuredly never have been written! Actually, the eager brute gripped my right shoulder between its jaws and started to drag me away, and as it did so I could hear the clatter of my horse's hooves over the stony ground as it raced away with the first lion in hot pursuit; itself in turn being chased by my dog Bull.
Meanwhile, the lion continued dragging  me towards the neighbouring Metsimetsi Spruit. I was dragged along on my back, being held by the right shoulder, and as the lion was walking over me his claws would sometimes rip wounds in my arms and I was wearing a pair of spurs with strong leather straps, and these acted as brakes, scoring deep furrows in the ground over which we travelled. When the "brakes" acted too efficiently the lion would give an impatient jerk of his great head, which added excruciating pain to my shoulder, already deeply lacerated by the powerful teeth. I certainly was in a position to disagree emphatically with Dr. Livingstone's theory, (1)  based on his own personal experience, that the resulting shock from the bite of a large carnivorous animal so numbs the nerves that it deadens all pain; in my own case, I was conscious of great physical agony; and in addition to this was the mental agony as to what the lion would presently do with me; whether he would kill me first or proceed to dine off me while I was still alive!
Of course, in those first few moments I was convinced that it was all over with me and that I had reached the end of my earthly career. But then, as our painful progress still continued, it suddenly struck me that I might still have my sheath knife! I always carried this attached to my belt on the right side. Unfortunately, the knife did not fit too tightly in its sheath, and on two previous occasions when I had had a spill from my horse while galloping after game during the Boer War it had fallen out. It seemed almost too much to expect that it could still be safely there after the recent rough episodes. It took me some time to work my left hand round my back as the lion was dragging me over the ground, but eventually I reached the sheath, and, to my indescribable joy, the knife was still there! I secured it, and wondered where best first to stab the lion. It flashed through my mind that, many years ago, I had read in a magazine or newspaper that if you hit a cat on the nose  he must sneeze before doing anything. This particular theory is, of course, incorrect; but at the time I seriously entertained the idea of attempting it, though on second thoughts I dismissed the notion, deciding that in any case he would just sneeze and pick me up again - this time perhaps in a more vital spot!
I decided finally to stick my knife into his heart, and so I began to feel very cautiously for his shoulder. The task was a difficult and complicated one because, gripped as I was, high up in the right shoulder, my head was pressed right up against the lion's mane, which exuded a strong lion smell ( incidentally, he was purring very loudly, something after the fashion of a cat - only on a far louder scale - perhaps in pleasant anticipation of the meal he intended to have) and this necessitated my reaching with my left hand holding the knife across his chest so as to gain access to his left shoulder . Any bungling, in this manoeuvre, would arouse the lion, with instantly fatal results to myself!
However, I managed it successfully, and knowing where his heart was located, I struck him twice, in quick succession, with two back - handed strokes behind the left shoulder. The lion let out a furious roar, and I desperately struck him again: this time upwards into his throat. I think this third thrust severed the jugular vein, as the blood spurted out in a stream all over me. The lion released his hold and slunk off into the darkness. Later I measured the distance, and found that he had dragged me sixty yards. Incidentally, it transpired later that both first thrusts had reached the heart.