What are you?

We waited about 10 minutes for this mysterious white thing to float down the stream so we could figure out what it was.  My friend, Sam, said "if that's a body part in a bag, I'm outta here."  I laughed but it did make the situation a bit more tense as we continued to wait.  Turns out it was just a collection of bubbles from the turbulent water up the stream.  Our imaginations sure have a way of running wild sometimes.