У вашего броузера проблема в совместимости с HTML5
Figured I'd upload this to help out console and potato PC peeps like me.
Couple of things to note:
Make sure to go in with 2 knives, don't use any to escape a grab or anything before the boss.
Make sure to grab the frag in the basement right before the fight and use it as he's about to break out of his first stun
When your first knife is about to break, let him grab you. More often than not he WILL grab you and this just ensures that you use the broken knife to escape out of it and you can use the stun afterwards for free damage from the new knife.
I haven't practiced it much but so far it's been 100% consistent.