Seeing eerie large dark brown smudge in the corner of rooms?

I'll see this brown smudge maybe like 2 feet long by 2 feet tall in the corner of a room. It'll be in any light condition and even in bright light. It's a circle and appears randomly. I can see it with both my eyes open or either one closed and looking through just one eye at a time.

I only recently decided to get closer to it. It's like a fog of brown and I can put my hands through it.

Anyone else know what I mean? Seen it before ? Is it normal ??