Just left a dental appointment that had me wondering... Do you close your eyes or keep them open while dentist is preforming procedure?

I choose to close my eyes...mostly because I once started to get the giggles while watching a hygienist working on me. Something about the way they were staring at my mouth at the time struck me as funny...which of course delayed the dentist work....and also made them laugh. A laughing dental technician with a sharp object is a scary thing.