Light danced on her dress.
When we use this expression, what is actually moving, making it seem the light is dancing?
A. the light (like candlelight)
B. the dress
C. either is possible depending on the context
C. movement is perceived, often not real. The light is moving somewhat in the case of a flickering candle (the source, the flame, moves so the light can appear to come from different angles), but sunlight dancing on waves is not due to sunlight moving, it is due to waves moving and the reflections changing location. When light is perceived to dance on a dress, it might be that the dress is causing the apparent movement, but it might be that the source is being affected before reaching the dress. Only context will really tell you if the appearance of dancing (light moving) is because leaves are shaking from a breeze and changing which sunlight gets to the dress (as one possible way to cause the light to dance), or if the dress is trembling and making light reflect from different spots on the dress (another possible way to make the light dance).
Her feminine physique swaying to the music under that dress that makes her soooo pleasing to the eye.