Sharpest straight blade you can find, cut them perfectly in half. Have to make sure the mouth and foot are both cut through the middle. Dip in an iodine wash afterwards, and replace in tank. Give it four weeks and they should be back to normal. Dont let any fish harass them in that first two weeks of healing.I'm not terribly knowledgeable of nems, but from what I understand, they need to split on their own and shouldn't be cut. The reason I say that is because I've only ever heard of people waiting for one to split and not ever once heard of someone cutting them in half.