What are these little semi-hard things that come out of my mouth when I sneeze?

I know this sounds really disgusting but there are these things that shoot out of my mouth when I sneeze. They are brownish-yellow, are shaped kind of like a little pyramid, and they smell like crap. I brush my teeth a lot, and I floss everyday plus use mouthwash. I always make sure my mouth is clean so I don’t understand why these things come out of my mouth. My sister thinks they a little things of plaque. I don’t believe her though because I never have plaque on my teeth because I brush them 3 times a day. Does anyone know what these things are, and how to get rid of them?