What's he saying?

Dominick's favorite new word these days is "up," which he's starting to use more and more, sometimes without any prompting. I'd say it's probably his first official word since "ah-oh," which was first used on February 1 (yes, I wrote it down!) and very frequently since then. So it's taken two months and lots of work, but Dom finally has another word in his repertoire of babbling and jargon.

Something else he's saying quite a bit is much less clear. It sounds like "ah, buh-buh," is always accompanied by a wave and is usually directed at a train, truck or other large vehicle. Is he saying hi to something? I'm dying to know what it is! "Hi, choo choo," maybe? "Bye, choo choo"? Or perhaps it's "hi, bye-bye." My vote is for the latter. How clever--a greeting and a send-off in one! Considering he says it to things that move, I guess it makes sense. This is the only sound he seems to associate with a particular thing or occurrence. I haven't been able to detect any other sounds yet that seem to mean something to Dom. Everything else appears much more random.