While a healthy dosage of guardedness is necessary in this game, one can't over look the fact that the dynamics of human interaction is an extremely complex matter, especially when the interaction takes place in the nude. Sparks can fly sometimes when flesh rubs against flesh hard under the right conditions. After all, these are hot blooded young girls in their sexual prime. As for the immediate triggers, there could be numerous possibilities. May be it's that time of the month. Good Times once remarked that he would mark down the day of the month when that happened and made a point of his return visit in that proximity. He has good batting average on that system. Or it could be due to what happened before her shift that day. We could go on speculating on hundreds of reasons. But it could happen for sure. And I would contend that it would only happen when she does have a soft spot for you or some kind of friendly affinity at the very least.
From personal experience, it did happen, though rarely. When it did, that lady would have my unflagging following for sure. To give in to an ugly old nerd, one can't but be touched by such generosity and deserves to be rewarded with steadfast loyalty. But we need to be clear-headed enough to realize that it's a rather serendipitous event and should not expect it to happen with regularity. But that day, that time, that lady, would be etched in the memory bank for our remaining days.
Ah, "these beads of coloured days" that decorate our lives.