From source:
 
Flash is a music pony, and although he has his favorite genre, he loves a little bit of everything. And his guilty pleasure is musicals, not even theater ones, oh no sir, movie musicals, no matter how trashy the plot is, if the songs are good for him that’s enough. It is not that he is a snob but others assume that kinda does not suit his style, so HIS BIG SECRET is whenever he is alone, cleaning or training he sings some little musical thing, and many times he gets carried away and ends up dancing, at least everyone has told him that he has a great talent.  
Have you ever been caught by my friends dancing and singing alone? to me yes and it was not very pretty XD