<P> Thoroughbreds is a 2017 American black comedy thriller film written and directed by Cory Finley, in his directorial debut . It stars Olivia Cooke, Anya Taylor - Joy, Anton Yelchin, Paul Sparks, and Francie Swift . The film had its world premiere at the Sundance Film Festival on January 21, 2017, and was released on March 9, 2018, by Focus Features and Universal Pictures . </P> <P> Thoroughbreds follows high - school student Lily (Taylor - Joy) and her emotionless friend Amanda (Cooke) as they scheme to kill Lily's stepfather (Sparks) via contract with a drug dealer (Yelchin). The film received positive reviews, holding an 87% approval rating on the review aggregator website Rotten Tomatoes, and a weighted average score of 76 out of 100 on Metacritic, indicating "generally favorable reviews". </P> <P> In suburban Connecticut, upper - class high schooler Amanda (Olivia Cooke) euthanizes her crippled horse with a knife, resulting in charges of animal cruelty . </P> <P> Some time later, Amanda arrives at the home of the more popular and academically - inclined Lily (Anya Taylor - Joy). The girls had previously been best friends but grew apart after the death of Lily's father . They meet under the pretense of hanging out and having a casual tutoring session, but Amanda knows that her mother (Kaili Vernoff) has paid Lily to socialize with Amanda . Lily denies being paid, but Amanda, left emotionless by an unspecified mental disorder, is unfazed . Lily meets with Amanda again, this time voluntarily, and they rekindle their friendship . </P>

What did amanda do to the horse in thoroughbreds