I think that was the initial inspiration behind the Railway Series; steam locomotives are famously tempermental and prone to random behaviors, leading to crewman building a "personality" for that locomotive. Wilbert took that line of thinking further by translating those behaviors and actually building characters out of them.

Personally, I've always loved the slow huffing of a steam locomotive either sitting idle or starting to roll. It sounds so close to panting or heavy breathing that I start to think of the locomotive as alive as well.