Why & How do I see this heart-shaped cardioid formed in my cup?

<p>I first got curious about this weird shape appearing in my cup a few months back, so I googled it and found it&rsquo;s called a &lsquo;cardioid&rsquo;. I knew that somehow it was formed inside this cup due to the reflection of light above it. But, I still didn&rsquo;t know how exactly was this shape generated. So the next thing I searched for was: How is a cardioid shape generated?</p> <p>So, by definition,&nbsp;<strong><em>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.</em></strong></p> <p><a href="https://medium.com/swlh/why-how-do-i-see-this-heart-shaped-cardioid-formed-in-my-cup-or-a-bucket-56330ef2a63a"><strong>Click Here</strong></a></p>