Acorn shaped UFO

So there I was, over at a friends the other day when I noticed these clouds that were multi coloured and decided to take a couple photo's. I swear this object was not there when I looked through the viewfinder. Not sure what to make of it. It does not look like a bug or bird and a bird I would have seen as I was snapping the picture. The one photo has an inlarged image in negative. Very odd indeed.