appearance: 9/13/90 Possum (5:47). Simpsons:   when a 10-note sequence from the opening of the  Simpsons  theme song is played, scream “ D’oh! ” like  Homer . First appearance: 9/25/91 Possum at 1:11 (the signal was also played earlier in the show during Reba but without the “D’oh!” response). Turn, Turn,