I like watching panels like this, with almost the whole cast. Every now and then they just start giggling and they basically look like they're having too much fun to call that work. This particular video includes some pretty hilarious moments with Chris Colfer, Kevin McHale, Jane Lynch, Darren Criss, Heather Morris and so on. There are also some MINOR SPOILERS. For example, Chris lets something slip, but as he says, "oh like you didn't know".
The embedded video above is just a summary. To watch the whole panel, click here for part one.