Everyone's feet are different. Generally, if you want the absolute most devastating tickling for feet, it's a hairbrush (with firm plastic teeth) (or anything with firm plastic teeth that you scrub with (shampoo scrubber, etc.)). The more firm the teeth, the better, because they dig into the skin instead of bending and gliding. You pull back the toes and scrub fast and hard. I've made grown women howl with this technique. (Adding something like baby oil that reduces friction would probably make it even more intense, though I've never tried.) In two rare cases, I tried hairbrushes on two women who didn't laugh at all and just said it hurt. One just wasn't ticklish. The other one just needed the right tool. I proceeded to lick and nibble and chew the balls of her feet with my teeth, and she fell apart! In short, you'll rarely go wrong with a hairbrush. If that doesn't work, try something else.