Back when Hangouts first debuted, it was quickly discovered that Google's messaging app included several easter eggs, ranging from ponies prancing across the screen, to a weird dinosaur hiding behind a house, to changing your chat's background color at random. Until yesterday, though, these bonus features weren't available for those using Hangouts on Android. As of the 2.1 update, users can make use of three easter eggs - one that will stream an infinite line of ponies across your screen, one that will send just one pony across, and one that will send an angry mob across, pitchforks and torches included. Take a look.
So far, these are the only commands we know of that will trigger easter eggs, and they appear to be the only surprises backed up by code we saw in our APK Teardown. Here's the list of commands in case you missed them in the animations above.
Missing from the list are /bikeshed, /shydino, and the Konami code. It's also worth noting that participants in the hangout won't see these effects (unlike /bikeshed, which changes everyone's background). That said, the Easter eggs are a nice touch, and can spice up even the most bland Hangouts conversation.
Update: It looks like we were mistaken in saying that /ponies and /pitchforks did not show up for other Hangouts participants. Those two effects are visible to all participants, though /ponystream (thankfully) is not.