A lipid droplet

You are convinced that this is a lipid droplet and you take out the slide to observe macroscopically as well. You also ask Prof. Johnson to have a look.

Prof. Johnson take a close look and comments.

Prof. Johnson: That was good idea lipid droplets are common contaminants with microscopy slides. In this case, however, this is not the main issue. Try to think of another explanation for what you are seeing.