I wish that this picture did better justice to the flowers themselves. It's not that Begonia flowers are that awesome -- we've all seen them, and I'm actually kind of sick of them, myself, because we've got some Begonia hanging baskets that I'm forever picking up after: they seem to always be dropping flowers on whatever's below them -- but this particular spray (technically panicle, the botanical term for a highly-branched inflorescence) of flowers was, I don't know, cooler than the picture makes it look.
Incidentally, I'd noticed while picking flowers up off the tables and the other plants and so forth that some of the flowers are lightweight and flimsy, basically nothing more than a few petals, while others have a large, heavy, solid base attached. I'd noticed this, but then never went any further with it to try to figure out what was going on, why they were making two different kinds of flowers.
I recently found out that this is totally on-purpose, and that the difference is just the difference between male flowers (flimsy) and female flowers (solid).
I'm not positive that first picture, way up at the top, has any male flowers, but Begonias are supposed to have both male and female flowers on the same plant. I'm also fuzzy about whether or not the number of petals means anything; it seems to vary a lot for no particular reason, but I've never made a careful study of that either.