Touched events work between any anchored part and at least 1 unanchored part, not two anchored parts. I assumed this was involving at least 1 unanchored part because more often than not, 2 anchored parts would not be moving.
This is true and what I meant. If one is not anchored, physics simulation!
Thanks, I was making an anchored part tween and trying to detect what is touching it. Strangely only the non-anchored parts were firing the .Touched signal.