I am playing RE4 pro mode and using knife only.
I already beat chief, scorpion looking boss, and Krouser with knife
but I couldn't beat the Salizar's right arm alien looking boss.
I knifed him for 35 min before my hand was nummed and I accidentally got hit
by him and died.

Chief took about 10~15 min, Scorpion took 15 min, Krouser took 20 sec, but this Salizar's right arm(?) is taking forever.

How many times am I supposed to knife the guy?
I actually used the gas to freeze him and kicked him 4 times and sliced him with knife about 150 times but he still didn't die.