Strange Gas spewing Mushrooms in Yard?

I was in my backyard, and noticed these little mushroom things. They're small and somewhat saucer shaped, with a brownish/gray coloring, and little lines all over them. Whenever you agitate them(even mildly), they spew this thick green gas. I may have breathed a small bit in, and was wondering what these things are. Is is like they're spores or something, or maybe even some kind of toxin?