The Sound Sword is a weapon the Earl of Lemongrab uses in "You Made Me." It produces a strong sound wave capable of knocking out its target. It also has the ability to inflict damage to weak objects; Lemongrab exploded Blombo's headphones and Finn's hat using the Sound Sword. He also shaved off Ice King's beard by the strong impact of his sound sword in "Mystery Dungeon." Lemongrab uses the Sound Sword to render his "unacceptable" subjects unconscious, so he can drag them into the Reconditioning Chamber. According to lead character designer Andy Ristaino, the Sound Sword is powered by the frequency of Lemongrab's screams, hence the "tuning fork" shape and the fact that Lemongrab screams as he uses it. In "The Mountain," Lemongrab 3 is shown taking out the Sound Sword when Lemonhope is ruling over Castle Lemongrab in the mirror, but puts it away when the third mirror opens. In "Come Along With Me," The Sound Sword can be seen amongst BMO's possesions in his house on Mount Cragdor.
The sword is long, flat and yellow and it has an edgeless, forked tip similar of a tuning fork. When unsheathed, the sword has a yellow aura surrounding it. However, in "The Mountain" it emits a white aura. When the Sound Sword's power is used, it emits circular sound waves at its target.
Appearances in other media
The Sound Sword is also used as one of Lemongrab's power-ups in Adventure Time Battle Party.