While the implementation is probably too aggressive, the search box is a good way to find other similar videos on YouTube. The player shows 6 results at a time, but you can navigate using the two arrows and you can view other thumbnails from the video before selecting it. To go back to the list of search results, click on the Search button.
The search box sits there, at the top of the video, to show that there is so much more to explore and this video is just the starting point. There's a small YouTube inside each embedded player.