Even with a hurt weight set to 0, the hurt dialogue seems to trigger about 20% of the time. It does this no matter the weight it is set to.

To recreate:

[hurt]
You shouldn't see this hurt-trigger line. Bug report time
[hurtweight]
0

I saw that about one in every five mobs I hit with the living weapon.

Hurt Weight appears to be the higher it is, the less often it is - its effectively taking 1/hurtweight, and undefined is always.