Inline media in Gmail chat
Chat in Gmail recognizes Google Video and YouTube URLs as media and automatically converts them to video inside your chat window.
This means you can use chat to send your friend a link to the video, 'Chat In The Name Of Love' (performed by a cast of Gmail engineers). In addition to the link, http://www.youtube.com/watch?v=ZVuXmmXOIj0, they'll see the video itself, and can press the play button to watch it inside the chat window.
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