Take a good look at the the legs in this photograph.
Do they appear to be shiny to you, as if they are wet or have oil rubbed on them? Would you believe that they are not oily at all? Instead, they are just a normal pair of dry legs with streaks and spots of white paint on them. Once you notice that the legs just have paint on them, the “shine” all of the sudden disappears.
This ambiguous optical illusion allows you to flip-flop back and forth from viewing the legs as shiny and viewing them as legs with white paint on them.
To see another optical illusion featuring legs, be sure to check out the Ambiguous Dancing Legs optical illusion.