Keenan Cahill, the lip-syncing YouTube sensation, has a new video out &amp;#8211; this one with noted backup singers Brian Wilson and Cody Ross. Lou Seal also makes an appearance as Keenan and the Giants perform &amp;#8220;Dynamite&amp;#8221; by Taio Cruz. Keenan, a 16-year-old from Elmhurst, Ill., has a rare genetic disorder known as Maroteaux Lamy Syndrome, [...]