Creation of this applet was inspired by a [url=https://twitter.com/gogeometry/status/942037810378366977]tweet[/url] from [url=https://twitter.com/gogeometry]Antonio Gutierrez[/url] (GoGeometry). [br][br]Note: This applet works best if the quadrilateral is kept convex. [br][br][b][color=#ff00ff]How can we formally prove the phenomena dynamically illustrated here? [/color][/b]