Weird energy thing with my legs

Yeah, it sounds familiar--I've been able to do the same thing since I was kind.  For me, though, the "flexing" happens in my chest--I've always been able to squeeze the front channels in my chest and make energy move up my system, giving me a deep sense of presence and heightened awareness.

My friend calls it the "Nintendo swirl," or something like that--he associated his ability to move energy as a kid with a sound effect in a video game.  It was only recently, when we were doing some meditations together, that I told him to try something and he said: "Oh, you mean the 'Nintendo swirl'..."!

In my experience, any energywork on the legs tends to deepen the grounding and the connection to the body--so I bet what you're doing is very related to grounding.

I'm an Aries, but I've been focusing on grounding a lot in the last few years. 

The solar plexus energy center is associated with fire and so is Aries--and I naturally began moving energy in that region.  Interesting.

I've heard that and experienced that--that energy enters on the left side of the body.  The left side is receptive, generally, and the right side is expressive.  But the right side can draw energy, too.

I've had pulsings like the one with your foot.  To me it sounds like an "energy knot" was loosening as a flow of earth energy was increasing in your foot.  And these little events can happen alongside everyday physical events, too--like the body trying to flush out metabolites from a hypertonous muscle.  It's all related.  Chances are that if there's an energy knot, there's some kind of physical knot and vice versa.

I feel reactions in my body as I do energywork all the time.  As you focus in on an area, blood flow will increase to that area and it'll heat up.  Sometimes, though, I just think an area is getting physically hot until I feel it and it's normal or actually cool. 

As for "normal" explanations for your foot experience, the feet collect a lot of body waste.  Laying on your back with your legs bent at 90 degrees on a chair, and with your tailbone barely lifted (maybe use a pillow under your legs), can help drain the feet and legs--as well as give your back muscles a chance to totally let go.  Do it for about 10-15 minutes.   

And you heard my abnormal explanation.  Robert Bruce has great exercises for dealing with blockages in the energy body.
His website is www.astraldynamics.com.  In a nutshell, though, just imagine a bright ball of energy and swirl it around your foot to help clear it out.