Flavor text. It's that fun quoted text at the bottom of most all Magic: The Gathering card that puts in a bit of character or context to the cards. Sometimes it's a quote from or about the creature on the card, sometimes it's from a book or other source material, and sometimes it's an actual quote from a real-life person such as, say, former U.S. President Calvin Coolidge.
While real-world quotes were eventually phased out in the early 2010s, there had been another, perhaps odder trend going on in early Magic: one word flavor text. Specifically, one word that is four letters. And, before you ask, no, not the "F" word.
Back in 1996, Mirage was being put together. Flavor text was being added to cards by the creative team, but one card, Ray of Command, had them stumped. They had no idea what to say, especially with so little space left in the descriptive text. Then head of Research and Development, Bill Rose, finally came up with a solution while looking at the card art and said "Heel!" because, hey, look at the art. Instead of some quote, it turned into a one word 'name that caption' contest.
Ray of Command's flavor text was so well liked that when Visions had a similar stumper with Magma Mine, they decided on a similar solution with the explosive "BOOM!"
It was off to the races from there.
For the next two years, every expansion had the running gag of one card having a one word quote. It went from a necessity to a highlight of the teams time to put one of these in there. They even became a punchline. Goblin Recruiter? Why put in a few sentences from a story or something when you can just say "Next!". Monstrous Hound? Why have some long explanation about scary it is when a simple "Stay!" suffices?
However, by 1998, Wizards of the Coast was getting a bit bored with the joke. As a grand finale they added in a giant "MOOO!" in, fittingly, an Unglued card: Hungry Hungry Heifer. Despite the fitting end, a lot of players soon noticed that the gag ended and kind of wanted it back. But everyone was soon caught up in Pokémon or the dot com boom or whanot and WotC, well, didn't bring it back.
That is until Time Spiral came out in 2006 and things got meta. Word of Seizing needed some text, and wanting to bring back the past, a single word was chosen yet again.
Just like U2 coming out with a new album or a sports team having a retro uniform night, Magic today will occasionally put one of these out both as a tribute, a gag, and to fill in the need for a tiny open area of flavor text.
Adventures in the Forgotten Realms even had one just last year with Split the Party having a "Don't" flavor text.
Not bad for a blurted out answer becoming a gag becoming stale and then a gag again.