Yup. She said that she thought she was going to be able to convince him that she wasn’t ticklish. He eventually went just a bit harder on her ribs, stayed a bit longer under her arms and she lost control.
Has happened to me many times. In fact it may happen every time, but because my premature laughter is so quickly followed by actual tickling it doesn't get noticed. But it happens a lot. My wife is so deftly devastating when she decides to tickle me that as soon as her fingers flex in my direction the giggles start burbling forth. And her sister, actually, has some kind of a weird air-tickling superpower -- I swear that as her hands advance on me I literally feel the physical contact second before she reaches me.
One of the few times the phenomenon actually got commented on and exploited, though, was on this occasion (linked) with my wicked frenemy Sarah, and in that case I think it's because I was particularly vulnerable and defenseless and she had made it clear she was in no mood to be merciful.
There's also "tickling " from across the room, like a knowing glance or a phrase that can make people crack a smile.
Even saying the word around some folks causes smiles and wiggles, let alone threatening to touch or actually touch.