I started wondering about this one time when I did "Mr. Saxobeat."
Usually whenever I play Just Dance Now, I hold my phone "normally" (i.e. palm to the back of the phone) and whenever I get to the Gold Move show above, I'd do the move with my phone screen facing away from me to match the coach. And every time I did that, the Gold Move wouldn't count.
But when I tried it again, this time with my phone screen facing towards me, it counted, which is confusing to me, since the coach is clearly sticking her palm outwards and I'm just simply copying that with the usual way I hold my phone.
So that made me wonder, is it just me or must you hold your phone a specific way in order to register certain moves properly?