The Prius Secret is that the engine is so loosely tuned it doesn't have much friction when starting, the oil also has the viscosity of colored water :)

Best of all it uses the EV motor and battery to crank the ICE engine, there's no separate weak-ass starter motor.

Had mine in -30C weather for a weekend, cranked it on monday night and it just - started. Like it had been vacationing in the French Riviera.

Compare that to my old Diesel VW, which - when cranked at the same situation - made a sound like someone was strangling a moose. I had two attempts to get it to start, then the battery would run out because of the friction caused by the thick-ass oil.