Turn on 'full raytracing', if you want nice reflections off the knife blade.
Anti-Aliasing 'Fast' is low quality (leaves much aliasing). That looks like about 1/2 your problem.
Also, you increase quality by changing the 'object accuracy' and 'shadow accuracy' settings (lower pixel = higher quality).
As always, there is a trade off between quality and rendertime.

Friends don't let friends use booleans.