I was digging a hole chunk out for my slime farm and I constantly noticed mobs jumping up and down which have been trapped in the hole that I made. I broke 4 blocks (bit enough for golem's hitbox) which I knew my iron golem would intercept in its path towards the witch. This caused the iron golem to attempt to jump up the now non-existent block which it failed at and kept jumping until I pushed it away from those broken blocks.

He died btw ;(.