Taro, pounded and thinned with water into a paste that behaves like a food, a fluid, and a personality test. The lab treats this as the island's least funded grand challenge: three laws so far, zero useful predictions, and units that sound official enough to win an argument.
Poi bought at "two-finger" consistency will be "one-finger" by dinner and "you'll need a spoon, sorry" by breakfast. This is the closest the island has to time travel.
You cannot dilute the purple out of poi. You can only dilute yourself out of a decent bowl of poi, which is how several family arguments begin.
Every poi order references finger count. Nobody has explained this to a visitor successfully on the first try, which is why this page exists and why you should send it to one.