I first got curious about this weird shape appearing in my cup a few months back, so I googled it and found it’s called a ‘cardioid’. I knew that somehow it was formed inside this cup due to the reflection of light above it. But, I still didn’t know how exactly was this shape generated. So the next thing I searched for was: How is a cardioid shape generated?
So, by definition, a cardioid is a curve traced by a point on the perimeter of a circle that is rolling around a fixed circle of the same radius.