Poor Antonio Salieri. Yeah, he had some success in his day, but let's just say you don't run across his works quite as often as some his contemporaries' these days. However, a soprano recently brought in a genuine Salieri aria from that big hit of 1785, La grotta di Trofonio. The aria, "Un bocconcin d'amante" is a two-parter; it starts with a very simple, stately tune and then concludes with a bouncy 6/8 section. As we were reading through it, about halfway through the fast section I found myself playing a little orchestral passage (with little interjections from the soprano above) that sounded suspiciously familiar. It took a few more minutes of rehearsing and mind-sifting to come up with it, but I finally made the connection. You can hear this brief excerpt by choosing the first item from the little custom-made player below. The second version there is just me playing it on the piano - and the third version is what I finally realized I was remembering. (Don't play the third one if you want to guess for yourself - spoilers below.)
It's not the most scandalous as tune thefts go, especially since it only occurs as a little orchestral transition in the Salieri - although, who knows, maybe this passage is referencing a tune that's more prominent elsewhere in the opera? I'm not planning to sit through this to find out, but maybe someone else knows more about it. Anyway, we know from watching Amadeus that Salieri attended a certain performance of a certain musical theater piece about a certain high-pitched wind instrument with certain magical powers. (Even the more reliable Wikipedia confirms that a Mozart letter places Salieri there.) That wasn't until 1791, six years after Salieri had premiered his little work about Trofonio's grotto.
Now, as you'll remember from the movie: Mozart faints, Salieri takes him home, and pretty soon we've got a dead composer on our hands. (Apologies if that spoils the movie for anyone.) Could it have been that Salieri noticed the moment (Track 3 above) when a comical birdcatcher sings about taking his own life - and takes a bit of Salieri's music to make his point? Maybe it was just an homage from one composer to another, maybe it was just a coincidence, but these are the facts of the case - and they are undisputed.
[Don't forget, Mozart's been known to steal from composers even more obscure than Salieri.]