It's magnae KyuHyun (and fans said that he couldn't dance. Pffffttttt)
My bias is saying that he is ohsoadorable with his embarrassed grins while adding Kyu-flavor into the dance solo.
It's up to you to decide whether he was proud or embarrassed.
And also how he managed to steal this golden opportunity from HanKyung, DongHae, ShinDong or SungMin.
Most likely he challenged his hyungs to Starcraft and won them.
Me loves smart-alec!kyuhyun. ♥
Apparently this wasn't the first time he attempted to take over Hyukie's dance solo because there were fan reports of how during one of the many practices of Sorry Sorry on some music show, Hyukie allowed him to dance during the dance solo while his singing-lines was stolen by the dancing machine. How cute.
Source for the video
Hope I did this right, first time posting ^_^*
The commentary are mine :)