The character of Mal Reynolds in Firefly obviously had a bit of Han Solo in him. But that's not what we're talking about here. It turns out that a small replica of Han in carbonite was on the TV show's set and occasionally made it into the broadcast footage.

I was just absolutely gobsmacked when I read about this on geek with curves yesterday, because I'm usually good at spotting anomalies like that and because I've seen every Firefly episode at least five times. Here's one picture (with Han identified by a red rectangle); you can see the rest in the original geek with curves post.

This gives us all an excuse to watch all the episodes again... not that we needed one.