A pair of disembodied feet, masks, or blurred face on the lee. Seeing the reaction is the point, anything that interferes with that makes the whole thing a total waste for me. Yes, some people can get past this but for me facial expressions and interplay are literally everything, and without this I might as well be listening to a laugh track and looking at a picture.
It doesn't bother me if the ler is in a mask or blurred, though I also don't really care one way or the other. I know for some people it's a total kill for them if they see a guy or a guy's face in the video, but I'm not really focusing on them so it doesn't matter.
It's also been my experience that in general, while women can do teasing well, the truly relentless stay on top of it attitude that will often produce the most authentic reactions from a lee are found more frequently in male ticklers than in female ones. Yes, I've seen exceptions, but very few of them. Gender is much less important to me than that they be relentless. Playfully relentless is probably my preference, but still, relentless.