To the OP: fluidity is believed to arise in response (hence, "receptive" sexual desire) to any of a wide range of stimuli. Among women, a very common stimulus is feeling an emotional connection with the person who otherwise doesn't fit with her.orientation. but there are many more and vary from.person to person.

I have had a hetero woman express a sexual interest in me. This woman had had fluidity a couple of times in her past that resulted in sexual encounters with women; she was fairly open to stimuli.

The scenario was as follows:

She and the new man she was dating were seated across from.me in his living room. The man and I were engaged in a fairly involved and complicated discussion of a matter in which I had some degree of mastery and in which he had aspirations towards. proficiency. She, an intellectually adept thinker in her own right, watched in interest and admiration.

Suddenly she seemed to sway a little and murmured something. We looked over at her. She said with some degree of surprise and excitement: " I was just overcome with a desire to sleep with Au Poivre; i feel very turned on right now."

I recognized it immediately as fitting with recent theories of sexual fluidity. I had been her friend for many years without either of us betraying any such interest in one another. I suspect there was a complex cocktail of factors involved including but not limited to her general susceptibility to intellectual stimulation and her intense intellectual and sexual admiration for her new lover which became conflated with her admiration and/or envy

Those are all guesses, obviously. I can't know her triggers any better than she could (fluidity likely happens on a subconscious level). But i do believe it was fluidity. I know her quite well and her proactive desires are pointed firmly toward men alone.