"Who is butchering music with my instrument?" a man asks that looks like he had a goat in his family tree. All below the belly is like goat, horns like a goat, a goatee and a lack of pants - face, trunk and arms look human. Save the ears, that remond more of elf. The upper half is also lacking clothes.
But at least his facial expressions seem easy enough to read and show something between disgust and anger. It is not clear how he appeared behind you unnoticed.