Question on snap shotting

Hello, I've been watching Quin69's stream and he does this thing with a weapon swap to quil rain/scorpion's call and then some interaction with fist of war causes his damage to spike up for a bunch of damage. I am just wondering how this interaction works if anybody knows? Trying to recreate a similar build but i haven't grasped how this mechanic works.

Thank you

its not about quillrain or scorpion's call. Ensnaring arrow make targets counted as moving even if theyre not. It persist through weapon swap and bleeding deels x3 damage against moving enemies