Finn's flute appears for the first time in the episode "Prisoners of Love." It is a woodwind instrument, crafted from the branch of a tree and poorly mended with tape, since Finn broke it trying to pick the lock to a sad ogre's heart (which wasn't shown in an episode). Finn plays it briefly, then throws it in an attempt to spear the Ice King, but it breaks apart in midair and falls to the floor before it can hit him. Finn seems to have a decent level of musical skill with it, but it is not the only instrument he plays.
When Finn needed to play music well in a battle against Death in "Death in Bloom," he notes that Jake is the musical one of the two. Furthermore on a wall with a great variety of musical instruments, Finn does not pick a flute or any similar instrument, meaning his flute playing has little significance, or else a flute-type instrument was unavailable. However, it is seen being played by an alternate universe Finn at the end of "The Lich." The flute has also appeared in the episode "Finn the Human," when Farmworld Finn shoves the flute in Tromo's nose, puffing up his eyeball when he played it.
In "Too Old," after Finn's plan to rescue Lemonhope fails and they imprisoned, Princess Bubblegum takes the flute out of Finn's pack and gives it to Lemonhope to play, hoping the music will lure the Lemongrabs into the chamber. Lemonhope plays it poorly, however, which nonetheless draws the Lemongrabs into the room. They find the sour notes pleasing, so much so that Lemongrab 2 happily releases the three.
In "Islands Part 3: Mysterious Island", the giant bear of an old lady named Alva sucks the flute into his nose.
Finn's flute appears to be a flute made of light yellow wood from a tree branch; it also has four keys and a lip plate, but unlike any other flute this flute doesn't have a tuning cork. The flute is damaged, with twigs sticking out of it and is messily "repaired" with white tape.
- In "Prisoners of Love," Finn plays his flute with both his hands facing backwards. Most flutes today are played with the right hand facing forward (with the pinky being the finger nearest to the end of the instrument), opposite the left hand.
- However, at the end of "The Lich," Farmworld Finn holds his flute on the left side of his body, as opposed to the right, as most flute players would hold it.
- It is also a mystery as to how he can play the flute with a claw-like hand; open-holed flute keys usually need to be covered by normal fingers for the instrument to make the correct sounds.
- Fionna also plays the flute. It can be seen in "Five Short Tables".