Although rabbits appear in all adaptations of Mo dao zu shi and have become a recognizable symbol of the series, The Untamed gives them by far the most actual screen time. Originally a mischievous gift and an early indication of romantic feelings in the novel, this increased presence of rabbits allows The Untamed to expand upon their symbolic meaning.
Rabbits — an inherently vulnerable and social prey animal — are used in The Untamed as a representation of the emotional vulnerability Wei Wuxian and Lan Wangji experience during the progress of their relationship. Rabbits do not appear at all during the portion of the story where their relationship is characterized by separation and conflict enforced on them by outside forces and Wei Wuxian's own secrets. Instead, the rabbits populate the quieter moments of connection. In a scene unique to The Untamed that differentiates it from the novel and other adaptations, Wei Wuxian and Lan Wangji first encounter the rabbits together after a mysterious force drags them into a cave: it is the sight of the rabbits wearing the Lan headband — a symbol of connection to the clan that can only be touched by one's parents and spouse — that inspires the two to use Lan Wangji's own headband to physically and metaphorically tie them together and protect Wei Wuxian. Afterwards, we see how the rabbits continue to represent a shared emotional connection during the lantern-painting scene when Lan Wangji smiles at Wei Wuxian for the first time.
Throughout the rest of the series, rabbits cause the two to fondly think of each other. Lan Wangji appears to worry that he has confessed his feelings for Wei Wuxian while drunk, juxtaposing a romantic confession with the reality of his statements that he likes rabbits and regrets not being by Wei Wuxian's side. The final appearance of the rabbits takes place the morning after the depth of Lan Wangji's devotion is revealed and Wei Wuxian reaffirms Lan Wangji as his soulmate, and echoes those sentiments: Lan Wangji puts his metaphorical heart in Wei Wuxian's hands, and in accepting it, Wei Wuxian finds that he's no longer afraid of what dangers the future may hold.