Courteney Cox and her dog may win the weird, viral Grimace Birthday Shake trend

What started as a limited-edition menu item to celebrate McDonald's beloved purple character Grimace's birthday has erupted into an inexplicably strange new viral social media sensation -- and now "Friends" alum Courteney Cox is getting in on the action.

The wildly popular "Grimace shake trend" that started on TikTok first shows customers taking a sip of the light purple berry-flavored Grimace Birthday Shake on camera before the video cuts to the person acting like they're in a scene from a horror movie, caught in the throes of death, or appearing like a zombie next to the remnants of the spilled specialty drink.

Even McDonald's has acknowledged the trend, posting a photo of Grimace on Twitter last month along with the caption, "pretending I don't see the Grimace shake trend."

Even some celebrities have gotten their hands on the shake just to partake in the viral moment -- including Cox.

Cox posted her own video on social media Sunday, a highly-produced version co-starring her sweet-turned-scary pup, Lily.

In the clip, Cox is seen holding a Grimace milkshake while sitting on her lawn, Lily by her side.

"So, apparently it's Grimace's birthday, and I've seen a lot of people drink this shake, and weird stuff happens -- but I've had half of it, and I don't feel anything," she says, before taking another sip. "I don't love it, but... I don't get the big deal."

Cox then stands up to walk away, dropping the shake on the lawn behind her, where it tips over. Lily begins licking up some of the milkshake herself, prompting Cox to walk back over and scold her.

"No, Lily, come on," Cox says, before her voice begins rising. "Lily, let go!"

Lily's tiny bark suddenly turns into a deep growl as Cox begins backing away in fear, looking at her dog, who has grown into a gargantuan beast.

"Lily!" Cox yells, running away in a panic as the video cuts off.

The hilarious take captured the attention of the official McDonald's TikTok account, which left a comment on the post, writing, "hi lily im grimace nice to meet youu."

Much like any viral trend on social media, it's unclear why the #grimaceshake trend initially took off, but for everyday fans of the golden arches and celebrities alike it appears to be a funky way to have fun with followers and friends: videos with the hashtag have garnered more than 1.6 billion views on TikTok alone, with more being posted each day.