I don't really slide my thumb on the blade at all. I just touch the thumb to the blade to feel for sticking. The funny thing is that, though I can't see any cutting at all, if I wash dishes after a long honing session, my skin swells up a little and then every single test becomes visible, revealing dozens of little slashes.

That stickiness results in the blade sinking imperceptibly into the skin even though you can't see it.