Anemones commonly reproduce asexually by basically splitting down the middle. This can occur when the anemone become stressed, when conditions become favorable, sometimes by accident, and sometimes on purpose. Many hobbyists help their anemones split by manually propagating them. A pair of tissue scissors or a simple razorblade, preferably a clean one, is all that is needed. Detach the anemone from the rocks and carefully cut down the middle, making sure to cut through the oral disk. Both anemone halves should recover from the propagation event fairly quickly, but the process can be fatal.
I don’t prefer to slice up anemones as a means of propagatation. I’ve always felt the best method is to let them split on their own.