From the Silly Panther Tricks department: open a Terminal window, and type - without pressing Return yet - killall Dock. Have another window from any app sitting behind this, and shift-click on that background window's minimise button, to make it shrink into the Dock in slow motion. Then press Return to execute the "killall". (It's quite safe, and won't disrupt anything. It's just cute. Use cmd-W to close the window, if necessary)
Yes, it works with a playing movie too. ^_^
-- Edit: the actual 3MB Flash file can be downloaded here. Yay!