
There are all sorts of quirks and eccentricities within FromSoftware games, both purposeful and accidental. One such singularity exists for Sif, the great grey wolf of Darkroot Garden and protector of Artorias the Abyswalker's grave.
During the fight, you might have noticed the playful dog jumping on your head amid its more harmful attacks, swinging around Artorias's sword to deal pain. There's a good reason for all the hopping towards you, and it’s not because director Hidetaka Miyazaki wants you to play fetch.
In the code for Sif’s moves, there's a small mistake involving two actions. As uncovered by modder kingbore, you have an attack triggering with the wrong animation. 'Att3011' is paired with movement 3009, a 180-degree flip. But they don't gel, resulting in a jump and twist that achieves nothing other than you getting a closer look at Sif's fur.
Meanwhile, there's another direction called 3009, that becomes a defensive maneuver wherein Sif leaps away if you get within stabbing distance. Pairing the proper action 3011 to the movement gives us a lunging stab. More effective and less nonsensical by some distance.
Sif’s second appearance, in the Dark Souls DLC set in Oolacile, where we learn more about Artorias, has everything functioning properly, with the bestest dog in all of FromSoftware lunging and stabbing as intended. The implication here is that the first encounter is hindered by a typo.
That's the prognosis by Dark Souls aficionado and YouTuber Zullie the Witch, and it's the most plausible explanation. Why it's never been addressed is another question. I choose to believe it's because the devs think it's cuter if Sif is trying to jump around with you. Can the next game include a boss who fetches, please?