Now that I have plenty of Invisible Shoe miles under my belt, I find that slapping sounds generally indicate that my lacing is a bit loose (especially in the forefoot part, from the ankle holes to the toes). Usually when I tighten up the laces (but it is not necessary to make them uncomfortably tight), my stride becomes much quieter.

I had something interesting happen during the first mile of so of the NYC Marathon Sunday (a mile-long climb to the bridge center followed by descent). I was venturing my first Invisible Shoe marathon, and for some reason noticed that my very carefully tied huaraches seemed to be landing unevenly. My right foot seemed to be landing more loudly than the left and I had the sense it was more in a plantar-flexed "tippy-toe" position when it did.

I should mention that my right leg has always been the short leg and that since I began barefoot running I've noticed the forefoot tends to land in an exaggerated supine position (with the outside of the foot overextending to meet the ground).

Long story short, I guess I had started the race with too chilled feet/legs combined with an insufficient warm up. Whatever problems I had on the Verrazano Bridge worked their way out once I warmed up, after easing up on the pace a bit and bending the knees more (Ken Bob Saxton's lifesaving advice, also Steven's recommended soft knees, soft ankles and hips). Big relief, let me tell you!

So the lesson is, first, make sure the forward lacing is taut enough. And the rear lace around the heel/achilles should NOT be pushing the foot so far forward that the toe knot is moving under the ball of the foot. If the lacing is good, I would hope any slapping is due to correctable form problems.

And that's one of my favorite things about Invisible Shoes: the audible feedback. As Steven has said, when something is wrong with your form, you will generally hear it — even more so than if you were truly barefoot. And when you get it right, you're as quiet as a ninja fox. More than once, people running alongside of me have mentioned that they never knew running sandals could make such little noise.

Also, I just wanted to mention that I suppose slapping could occur if the sole is a bit too big for the foot and could benefit from a little *careful* trimmimg with the scissors. If this seems to be the case in a glaring way, let the dust- and wear-pattern be your guide but err on the side of too much rather than too little sole.