The sheet music.
That's My Horse is a song played in "Wish You Were Ed". The tune is a folk song Edd ended up settling on in a music book when Rolf requested the "Song of Rolf's Village." It is played by Edd on a bottle labeled "broth," with an unseen accordion entering a moment after the song starts. The song is first played by Edd and then by Rolf.
Participants are to say to the others "That's my horse!" before causing intentional pain to them. When Rolf learned that the Eds lied to him about being in the Old Country, he got revenge by playing the song but with increased levels of severity, causing Ed to injure Eddy and Edd.
The notes in the song are shown in a music book. A treble clef with chicken leg noteheads is shown on a staff that has 6 lines instead of the standard 5, making it difficult to determine what the notes are. While there is no evidence that they are the actual notes for the song, they are likely intended to show the part Edd plays on the broth jar. The whole staff is shown with a blue horse behind it.
Video[]
That's my horse