The killer first brings up the idea of a "forest adventure," in a text to Travis in late April (iirc). Travis calls it something like that when he replies to a text she's sent, and says the idea sounds good.
That's the 10 page rape fantasy she sends to herself on May 2 , possible reworked from the emails she said she sent him late night May 1.
On the sex tape (first time I've actually listened to the whole thing), right after they talk about her butt and his endurance, there is one of what seem to be many awkward pauses.
Travis mumbles something that is hard to hear, but after rewinding 3 times I heard it. He says that he is "intrigued by that forest adventure."
It takes a second for her to hear what he said too. And oh my did she change the subject as quickly as she could, to talk about his itinerary, was he coming there before Cancun, etc.
Interesting, eh? What he was saying was that it was HER idea. You would think in the middle of a phone sex call before they got to it that she would want to discuss that idea of hers. No, huh, killer? Why not?