Cheryl had cum twice already backed up to the strong jets of that tub. Now she's on display for the neighbors of the rented house. Plain view from three sides. I wanted her to put on a show and she did.
It was dark enough to make her more visible if the hot tub room's bright lights were turned on. Her show was clearly visible then and they could all watch her masturbate. As she began having orgasms and twisted around, they must have known she was cumming.