McDonald’s is behind one of the summer’s most coveted treats, which has put its mascot Grimace at the forefront of a viral trend.

And it all started with what appeared to be a simple promotion in June to celebrate the 52nd birthday of the Ronald McDonald gang’s furry purple member: a purple milkshake (available for a limited time, natch). As luck would have it, the milkshake has made TikTok bleed purple as internet denizens have taken the concoction from tasty treat to horror prop in due fashion.

The fad is confusing to some and delightful to others. Here’s how it happened.

What even is Grimace?

Grimace is one of McDonald’s hype house of mascots, which includes Ronald McDonald, Mayor McCheese, The Fry Kids and Birdie the Early Bird.

He was introduced first in 1971 as a more sinister character named Evil Grimace. He was inclined to steal people’s milkshakes, much like his counterpart Hamburglar, who steals hamburgers.

According to McDonald’s, Grimace is supposed to be the “embodiment” of a milkshake. The grinning purple blob has commonly been interpreted by others as a taste bud.

“The original Grimace was scaly, mean-looking, had four arms, and had no charm whatsoever. He scared kids,” Roy Bergold Jr., the former vice president of advertising at McDonald’s, wrote in QSR Magazine in 2012. “We changed him to a soft, plush, two-armed blob of a sweetheart who only wanted McDonald’s milkshakes and to hang out with Ronald [McDonald].”

While the famed clown and other figures were approachable, Evil Grimace just wasn’t bringing in the crowds. But now he’s the internet’s beloved furry friend.

“Grimace is from Grimace Island and comes from a huge family [including his Grandma Winky, aunts Millie and Tillie and his Uncle O’Grimacey!],” McDonald’s said in a statement in June . “Our timeless bestie has become a fan-favorite known for his signature fuzzy purple look, friendly and playful personality, love for shakes, and of course — ambiguous nature. What exactly is Grimace? Perhaps we’ll never know…”

Why is Grimace all over the McDonald’s socials?

Apparently, Grimace has a pretty involved fan base. In early June, McDonald’s changed its profile photos on TikTok, Twitter and Instagram to a photo of Grimace staring at a pale purple shake topped with whipped cream and a straw. The next day, it was announced that the change was in honor of Grimace’s birthday. The exact date of his birthday remains unknown.

“i finallyy got my own grimace meal and purple shake :),” the account posted with a picture of him hanging out of an 80’s-style car. It was announced that a special meal in celebration of his 52nd birthday would be available — while supplies last — starting June 12.

In addition to adding a special meal for the birthday blob to the menu, the company launched a video game in which Grimace travels around the world rounding up his pals to cut his birthday cake. And there’s exclusive merchandise, including bucket hats, a pool float in his shape, beanies, socks and T-shirts. Instead of “birthday gifts,” McDonald’s encourages people to donate to “Grimace’s favorite charity,” Ronald McDonald House Charities. And that leads us to …

… the ‘Grimace Shake Incident’? Is it really making people sick?

No. The absurd video trend coming out of the craze — called the “Grimace Shake Incident” by some — may unsettle people unfamiliar with Gen-Z’s comedic lexicon. Online, social media users have jokingly exaggerated the effects of drinking the shake.

On June 14, author John Paul Brammer tweeted that drinking the Grimace shake “binds you to his will.”

The same day, user @notsofiacoppola joked that “there’s a grimace in the back of every mcdonalds that is screaming in pain as they milk him” to produce the shake.

TikTok user @thefrazmaz (Austin Frazier) seems to be the first person to make the slightly disturbing Grimace Shake Incident, on June 13, Stay Tuned NBC reported on their TikTok account. Taking inspiration from the similar Spider-Verse burger trend earlier this year, the format depicts people excited to try the pale purple drink, wishing Grimace a happy birthday. Once they take a sip, the video quickly cuts to a scene of them passed out. Locations vary but include abandoned buildings, a playground, in a tree, across a car hood or in a trunk with the shake spilled or splattered on themselves or nearby.

While the TikToks vary in production value, some are incredibly cinematic, using drone shots, CGI and DIY Grimace costumes.

“#grimaceshake” has amassed over 1 billion views on TikTok, with some celebrities including Courteney Cox getting in on the action.

What does the milkshake taste like?

The pale purple shake was part of the Grimace Birthday meal, which came with a 10-piece chicken McNuggets or Big Mac and a side of fries. The Grimace Birthday Shake paired vanilla soft serve and berry flavors, and is “inspired by Grimace’s iconic color and sweetness,” McDonald’s said in the news release.

What has McDonald’s said about the meme?

The shake has been catching steam but not in the way McDonald’s may have anticipated.

On June 28, the McDonald’s TikTok account wrote in a caption of a video of Grimace covering his eyes with his hands, “woww lots of peoplee r tryingg the grimace shake.”

“meee pretending i don’t see the grimace shake trendd,” text imposed on the video read.

McDonald’s could not immediately be reached for direct comment.