Twitter has quietly begun testing of embedded videos in tweets. In a tweet posted on Wednesday morning, CEO Dick Costolo  posted video  of himself making steak tartare, with the video embedded within the tweet through video service Vine. On Thursday morning, Costolo posted another tweet urging Twitter users to download Vine .
This past October, Twitter acquired Vine , which stitches together mini-montages of users' mobile video clips. Fast Company sat down with Costolo  to discuss his leadership strategy in November.