Why is the dog's head missing in Portrait of Yvonne Duchamp-Villon by Marcel Duchamp?

I found it hard to recognise it as a dog at all, but I didn't see the original. Here it is if anyone else is wondering

http://visitors.ringling.org/eMuseum/html/media_en...

Yes it was done purposely. In many of his paintings. Duchamp is regularly described as a sadist and nihilist. He deliberately obliterated or spoiled parts of his paintings. A Dadaist, he was protesting against the act of painitng and wanted to destroy the idea of art and the possibility of an aesthetic experience. By the way, Yvonne Duchamp-Villon was the artist's sister-in-law.

Yvonne Duchamp Villon was his neighbor but Marcel Duchamp hated his dog so he cut off its head. Then he painted a picture with the dead dog in it.

Dogs classically refer to ideas of fidelity in regard to symbolism