What is Reddit's opinion of Cows?
From 3.5 billion Reddit comments

By popularity on Reddit, this product is:

6 reviews of this product found across Reddit:

(On mobile so hopefully my formatting isn't borked!)

Everyone's nightmare fuel is different, of course, but here are a couple that gave me some freaked out nights for very different reasons:

COWS by Matthew Stokoe This book is sick. But it's also well written, which is what takes it beyond shock value. Pretty much everyone who has read it can recite a scene that really messed them up.

THE GIRL NEXT DOOR by Jack Ketchum I took this out of the library several years ago. I had to renew it multiple times because I could only read it in small sections. It made me cry more than once and I definitely had nightmares. I've never read any other Ketchum, but I've seen folks around here saying he's got other books that will mess you up. I know OFF SEASON and THE WOMAN get mentioned quite a bit; maybe someone who's read those can chime in.

HOUSE OF LEAVES by Mark Z Danielewski This one is divisive, but it's one of my favourites. I buddy-read it with several long distance friends in various time zones (I'm in Toronto, and they were in Ohio, California, Washington State, Colorado and Australia!), so we spent many nights texting about how creeped out we felt being home alone while reading it. We likened it to a long, terrifying drug trip.

HAUNTED by Chuck Palahniuk A collection of short stories that have a through line narrative. Each story is about/written by one of the characters, and each is its own kind of disturbing, creepy, or upsetting.

I used to moderate a massive book club on Livejournal (!!) that was devoted to the most disturbing books in the world; I wish we could've migrated all of the 4,000 members to Reddit successfully, because we had a hell of a list! (ETA: here are a few posts about books with a captivity theme - THE GIRL NEXT DOOR is mentioned a couple of entries down. I'm amazed our massive archive is all still intact! You can search it by tag, too.)