There’s nothing special about horses. You could just as easily play Z-E-B-R-A or H-U-M-A-N, and the game would play out exactly the same. Players at home might be familiar with P-I-G, a game that’s identical to H-O-R-S-E, except you lose after three letters instead of five. This is perfect if you’re in a time crunch, or you otherwise lack the commitment to play for five whole letters.
But what if you’re a real power player? What if you have all the time in the world? What if you want to play H-O-R-S-E, but make it even longer?