Special Relativity - Part 3: Symmetry in time dilation

This is the third video in a series on the special theory of relativity.
In this video I give some explanation and animation on the symmetry of time dilation: when someone is moving at a constant speed relative to me then that someone's time runs slower as compared to mine, but that moving someone can say the same of my clocks!
That seems strange, but the animation shows how this can actually be correct according to the special theory of relativity.
In addition I show that this symmetry is no longer in effect if the one that's moving relative to me changes his movement by returning to me (so called twin paradox): upon returning less time has elapsed for him as compared to the time that elapsed for me.