This clever loop starts with any initial instance of lifegain, which immediately prompts Spider-Man, Peter Parker to place a +1/+1 counter on Scurry Oak. That counter in turn causes Scurry Oak to trigger and create a 1/1 Squirrel token, and the arrival of that new token makes Impassioned Orator trigger to grant you 1 life. Because gaining that life starts the whole cycle over again, the engine sustains itself indefinitely to yield an army of tokens, boundless life, and a towering creature covered in +1/+1 counters.