Lyric Opera has been posting clips of last season, both to their website and to YouTube. Look!
This may sound strange, but I keep looking at their stomachs - especially near the end of the clip, where you can really see them - and how they use their breath to sing, low in the abdomen. During Lucretia, the only person whose stomach was really visible like that (well, beneath the sweater) was the Female Chorus, and I watched hers too. Let's face it, when it comes to studying voice and vocal technique, I'm an equal opportunity stomach-watcher.
Edited to add: In case that link above stops working, here it is in another format: