Warning: Contains spoilers for Yellowjackets season 1.
In the Yellowjackets season 1 finale, Simone finds Taissa’s shrine hidden in a secret room off their basement, and the altar appears to contain a human heart. Throughout Yellowjackets there is a looming question of whether the supernatural elements of the show are real, or merely the way the characters see the world. Taissa’s shrine drives at the heart of this question, as to whether the apparent sacrifices she has made have had a real effect or merely steeled her resolve.
In Yellowjackets episode 9, Shauna (Melanie Lynskey) stabs her lover, Adam (Peter Gadiot), and kills him, requiring four of the survivors from the wilderness to come together and get rid of the body. At the end of Yellowjackets episode 10, Taissa (Tawny Cyprus) is listening to the results of the election and learning that she has won, while Simone (Rukiya Bernard) is getting some things from their house while Sammy (Aiden Stoxx) plays upstairs. She notices some blood by a grate and goes through it to find an altar that is marked with the symbol from the wilderness and contains Sammy’s broken doll, their dog’s head, and a heart of unknown provenance.
The heart on Taissa’s altar in Yellowjackets might be thought to be from the family dog, Biscuit, as with the dog’s head; however, it is too large to be a dog’s heart (and it’s clearly much smaller than the bear heart that Lottie, Van, and Misty offer as sacrifice in the wilderness). It seems most likely that the heart in Taissa’s shrine is indeed human. As Simone finds fresh blood by the grate that hasn’t dried yet, it is likely that the heart has only been added to the shrine recently, and therefore, with the timing of it, it seems most likely that this heart belonged to Adam before his demise.
If this is the case, then Taissa must have gone to quite some lengths to attain it. When the group were disposing of Adam’s body in the Yellowjackets season 1 finale, Misty (Christina Ricci) and Taissa were in charge of cleaning up the blood, while Shauna and Natalie (Juliette Lewis) cut the body up and take the majority of it to be buried in a suitcase. This would not leave much opportunity for Taissa to take Adam's heart without anyone noticing, which means that she must have gone back and dug Adam’s body after the others had left to be able to get his heart. Misty tells Natalie and Shauna where to bury the body in front of Taissa (Hacklebarney Park), so she knows where to look, but it must still have been a difficult undertaking.
If the heart did not belong to Adam, there are some other possibilities, but none are as plausible. The only other person mentioned to have died in the present day of Yellowjackets is Travis, who died across state lines, and if his heart had been removed it would have been hard for the police to rule it as a suicide. While she might have murdered her political opponent, Phil Bathurst, there’s no evidence that he is dead when the election results are being read out. Therefore, narratively, it really only makes sense if the heart on Taissa’s altar in Yellowjackets was Adam’s.