The Man with Two Brians
S7, E5: Realising that Brian may be getting old, Peter gets a newer, happier dog who the Griffins love, prompting Brian to leave. However, things go awry when the "new Brian" crosses the line and humps Stewie's favourite toy.

S7, E5: Realising that Brian may be getting old, Peter gets a newer, happier dog who the Griffins love, prompting Brian to leave. However, things go awry when the "new Brian" crosses the line and humps Stewie's favourite toy.