These don't look like any of the six species of microorganisms that are supposed to be in my yogurt.
This first one was in a previously opened container that I should have finished it last week, so it's totally my fault. Fungus?
/After ditching that one, I opened a brand new container that doesn't expire for two weeks, and I see this:
Looks more like bacteria, but again not one of the species that's supposed to be there. This one is more interesting, because either it was introduced at the manufacturer, or else the seal had a gap... so the species is alien to my immediate home environment. There's a colony growing in the middle of the yogurt on top, too. Must have spread from the colony (somewhat visible) on the underside of the seal.
I should have waited before dumping the first yogurt out. I could have mixed the colonies together and let them duke it out. :)