Round smoke ball under the work desk

I was working, it was pass two am. at night. I noticed there was some thing at my feet. I looked at my feet, saw a round smoke ball. The smoke in the ball was moving in circle. I was curious and continued observing the ball of smoke which is about 40cm in diameter. A face came out from the ball toward me. It was an angry face, the face the get back into the ball and vanished.