This free Halloween-themed piano piece uses 5 notes in both hands - F, G, Ab, B, C 
 
The use of the minor 3rd and augmented 4th (tritone) adds to the eerie sound of the piece.
 
"Trick 'n' Treat" ends with an octave jump (lower in the left hand, higher in the right hand) and a chord of a minor 2nd in the right hand to mimic a scream!