Harry's Creatures, Outside the Cup

Video 4 of the experiment with Harry the Rock.
This short video is only focused on 1 drop which came from one of the cups (video is 2:40 total time).
I noticed a brown spot on a piece of the glass I use to keep the microscope as stable as possible while I'm recording.
The glass sits directly on top of the cup's lid and the microscope sits on the glass.
When I noticed the brown spot I looked at it under the microscope and this is what I saw