Noobie Question - is this effect hard to do?

I just started using flash and there is an effect I keep seeing that I love.
I was jusr wondering if this is hard to do and if someone can explain to me how to do it. If you go to www.tokyoplastic.com and enter the site. It’s one of the first animations that happens. When the bouding box opens up and the edges feel like they bounce into the form of the rectangle (does that make sense). Hopefully someone understands what I mean. Any help would be appreciated.