In the episode where Brian dates a girl that says she's an atheist (but ends up lying to get around), Brian talks to Stewie while starting his second gen Prius, but if you listen carefully, you can hear the gas engine rev up (like most cars do when you start them up)

Those who drive a Toyota Prius (or other hybrid vehicle) can tell you that when starting it, the gas engine doesn't start up unless you are in drive (at a certain speed), or if you are in the battery charging mode, Priuses start very quietly, and do not have that revving sound