Re: Why does a choo choo (steam loco) make a choo choo sound?

If you are asking about the source of the sound, it's steam escaping through 
small holes. These holes were deliberately placed to put an upper limit on steam 
pressures inside the cylinders of the locomotive.

If you are asking why we spell the sound "choo choo" that's a question for
a linguist! Onomatopoeic word origins are a bit complex; for example, the "sound 
a dog makes" is, I gather, spelled rather differently in French and German than 
in English.

                                          Dan Berger
                                          MadSci Administrator