The video was posted to TikTok on October 21 by Kaci Jane Hansen (@kacijanehansen), who wrote: “when the leech fell off my thumb & escaped leaving behind a trail of blood LOL.” The post has racked up 25 million views and nearly 3 million comments.

“I was in an ATV accident & my thumb was completely severed off my hand & they reattached it & to help with the circulation they used leeches,” Hansen explained in the comments section of the video.

The trail of blood begins in Hansen’s bed, where Hansen is sitting. Noticing that the trail continues underneath the bed, the person recording the video walks to the opposite side of the bed and finds the leech slithering against the baseboard of the room’s back wall.

“Look at him—he’s huge,” says someone off-camera. Meanwhile, someone else can be heard laughing and saying “oh my god.”

The first part of the video is set to a popular TikTok sound, which features the actress Sarah Paulson yelling: “Help! He’s escaping! The killer is escaping! Help me!” The sound originates from an episode of American Horror Story: Asylum.

The TikTok sound stops, however, as the camera approached the leech.

Many commenters couldn’t believe that some doctors still use leeches for patient care.

“I thought we left leeches in like 1782,” said quaysadilla.

“I thought this was a myth!!! They really use them,” added ophelia.

According to University Hospitals (UH), leech saliva can keep blood flowing.

“Leech saliva contains hirudin, an anticoagulant and anti-platelet agent that works to prevent blood clots and reduce the amount of congested blood in the tissues,” said UH on its website.

“Other chemicals in leech saliva keep the blood flowing in the damaged area, even after the leech is detached, allowing time for new veins to grow and the existing ones to widen and accommodate more blood flow,” the website said.

The healthcare provider also explained that leeches are specially bred for medical use and are only used once.

“After they have fed and cropped off the patient, they are anesthetized and disposed of as medical waste,” UH concluded.

Viewers were shocked by the video.

“Somebody call McDreamy STAT,” joked the official Duolingo account.

“That’s literally the most traumatizing thing I have ever seen in my life,” added Hintzkanen.

Shii Among the Jungle said: “This feels like an actual AHS scene.”