After she figured it out, the situation was not that hard to understand. If intimate activities were delineated according to levels, sex would naturally be the highest level and lower than it would be kissing, hugging, and holding hands.
Hugging and holding hands were out of question because they might occur too accidentally, like someone might reach out to steady you when you tripped and fell. In fact, these activities might be considered a cultural reaction for the alien race.
So, it was understandable that these two interactions would not influence the sex transformation. However, kissing was obviously a sign of intimacy. If intercourse was the concrete condition to stabilize one's sex, a level 1 intimate interaction could be seen as a pseudo-trigger.
The effect of a pseudo-trigger was not permanent, so without a final condition to follow up, the sex swap would return to its original state.
