Normally, poo is any number of shades of brown. But, the video explains, that's all because of one chemical: the pigment stercobilin. It's created along the digestive tract when your gut bacteria metabolize the yellowish-green bilirubin in bile. The biproduct formed here reacts with oxygen to create stercobilin. So, if your number-twos look like you swallowed your lawn, that might be because they're traveling through you too quickly — before your gut microbes have time to eat their way through all that bile.
There are plenty of mostly-harmless reasons why this might be happening (maybe you're a bit hungover or getting over some food poisoning). Or, even if everything's happening at the right speed, you still might be going green if you just ate a bunch of food with green dye in it — or blue and yellow dyes together. (Yep, the rules of kindergarten color-mixing hold true in poo, too.) Of course, if you're pooping pea-colored hues every day, go see your doc. But, if it's a one-time phenomenon, there's no reason to stress. Who wants to wake up and see boring-old brown in the toilet every day, anyway? A little variety is good in life.