Zend_Feed entires and colon separated keys

I've created a function that consumes an RSS feed from Flickr using Zend_Feed.Unfortunately I am struggling to extract some keys!

I can get the < title > and such by echoing

$entry->title();

But how can I echo out something like < media:thumbnail >?

I'm sure there's a completely simple way of doing this but I can't for the life of me figure it out!

Here is an example entry

<entry><id>http://gdata.youtube.com/feeds/api/videos/T-Pq6QSeH7A</id><published>2009-09-16T11:51:20.000Z</published><updated>2009-09-18T02:37:35.000Z</updated><category scheme='http://schemas.google.com/g/2005#kind' term='http://gdata.youtube.com/schemas/2007#video'/><category scheme='http://gdata.youtube.com/schemas/2007/categories.cat' term='Games' label='Gaming'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='torchlight'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='vanquisher'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='mmo'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='mmorpg'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='massively'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='multiplayer'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='online'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='game'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='mmohub'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='hub'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='forums'/><category scheme='http://gdata.youtube.com/schemas/2007/keywords.cat' term='reviews'/><title type='text'>Torchlight - Vanquisher Gameplay</title><content type='text'>I'm so excited to reveal the latest trailer for Torchlight, featuring the third class, the Vanquisher!</content><link rel='alternate' type='text/html' href='http://www.youtube.com/watch?v=T-Pq6QSeH7A&amp;feature=youtube_gdata'/><link rel='http://gdata.youtube.com/schemas/2007#video.responses' type='application/atom+xml' href='http://gdata.youtube.com/feeds/api/videos/T-Pq6QSeH7A/responses'/><link rel='http://gdata.youtube.com/schemas/2007#video.related' type='application/atom+xml' href='http://gdata.youtube.com/feeds/api/videos/T-Pq6QSeH7A/related'/><link rel='http://gdata.youtube.com/schemas/2007#mobile' type='text/html' href='http://m.youtube.com/details?v=T-Pq6QSeH7A'/><link rel='self' type='application/atom+xml' href='http://gdata.youtube.com/feeds/api/users/mmolifetv/uploads/T-Pq6QSeH7A'/><author><name>mmolifetv</name><uri>http://gdata.youtube.com/feeds/api/users/mmolifetv</uri></author><gd:comments><gd:feedLink href='http://gdata.youtube.com/feeds/api/videos/T-Pq6QSeH7A/comments' countHint='0'/></gd:comments><media:group><media:category label='Gaming' scheme='http://gdata.youtube.com/schemas/2007/categories.cat'>Games</media:category><media:content url='http://www.youtube.com/v/T-Pq6QSeH7A?f=user_uploads&amp;app=youtube_gdata' type='application/x-shockwave-flash' medium='video' isDefault='true' expression='full' duration='97' yt:format='5'/><media:content url='rtsp://rtsp2.youtube.com/CigLENy73wIaHwmwH54E6erjTxMYDSANFEgGUgx1c2VyX3VwbG9hZHMM/0/0/0/video.3gp' type='video/3gpp' medium='video' expression='full' duration='97' yt:format='1'/><media:content url='rtsp://rtsp2.youtube.com/CigLENy73wIaHwmwH54E6erjTxMYESARFEgGUgx1c2VyX3VwbG9hZHMM/0/0/0/video.3gp' type='video/3gpp' medium='video' expression='full' duration='97' yt:format='6'/><media:description type='plain'>I'm so excited to reveal the latest trailer for Torchlight, featuring the third class, the Vanquisher!</media:description><media:keywords>torchlight, vanquisher, mmo, mmorpg, massively, multiplayer, online, game, mmohub, hub, forums, reviews</media:keywords><media:player url='http://www.youtube.com/watch?v=T-Pq6QSeH7A&amp;feature=youtube_gdata'/><media:thumbnail url='http://i.ytimg.com/vi/T-Pq6QSeH7A/2.jpg' height='90' width='120' time='00:00:48.500'/><media:thumbnail url='http://i.ytimg.com/vi/T-Pq6QSeH7A/1.jpg' height='90' width='120' time='00:00:24.250'/><media:thumbnail url='http://i.ytimg.com/vi/T-Pq6QSeH7A/3.jpg' height='90' width='120' time='00:01:12.750'/><media:thumbnail url='http://i.ytimg.com/vi/T-Pq6QSeH7A/0.jpg' height='240' width='320' time='00:00:48.500'/><media:title type='plain'>Torchlight - Vanquisher Gameplay</media:title><yt:duration seconds='97'/></media:group><gd:rating average='5.0' max='5' min='1' numRaters='1' rel='http://schemas.google.com/g/2005#overall'/><yt:statistics favoriteCount='0' viewCount='24'/>

I would like to extract the first thumbnail url from the entry.