Grégoire Blanc is a French prodigy (he's not twins - it's just video trickery) who loves the Theremin - the mysterious 20th century instrument that produces sounds from radio signals generated by the position of one's hand in an invisible field. Grégoire has appeared on French TV, and his YouTube channel is one to cherish. Here, he performs Passacaglia for Violin and Viola by Johan Halvorsen, based on Passacaille (No.6) from Suite in G minor by Handel, on Theremin and the equally haunting musical saw.
It's worth mentioning that some people think his intonation (a very tricky thing on a Theremin) is too perfect, and that Grégoire uses pitch-correction software. I reckon it's more likely he records complex pieces in sections and stitches them together. Regardless, the result is very pretty.