[Flash 10 is required to watch video.]renderVideo(“video_player_6565623396”,’http://api.tumblr.com/video_file/6565623396/tumblr_lmupc4k1Y21qzkgnb’,500,393,’poster=http%3A%2F%2Fmedia.tumblr.com%2Ftumblr_lmupc4k1Y21qzkgnb_r1_frame1.jpg,http%3A%2F%2Fmedia.tumblr.com%2Ftumblr_lmupc4k1Y21qzkgnb_r1_frame2.jpg,http%3A%2F%2Fmedia.tumblr.com%2Ftumblr_lmupc4k1Y21qzkgnb_r1_frame3.jpg,http%3A%2F%2Fmedia.tumblr.com%2Ftumblr_lmupc4k1Y21qzkgnb_r1_frame4.jpg,http%3A%2F%2Fmedia.tumblr.com%2Ftumblr_lmupc4k1Y21qzkgnb_r1_frame5.jpg’)

The Reeder for Mac site leverages some impressive HTML animation tricks.

Update: Thanks to Brett Taylor for this one: just like on a Mac, you can Shift-click to experience the animation transitions at roughly half speed.