What you see may depend on your life experiences.
This image appeared on a German postcard as early as 1888.
If you look closely enough, you can usually see both figures—a young woman and an old woman. But you can see only one at a time. The brain locks into one interpretation and can’t see the other at the same time.1,2
Can you imagine a situation in your pharmacy in which locking on to one image, instead of another, could lead to problems?