The amount of milkshake in their glasses the first time Curtis and Jocilyn are in the Dreaming Tree.
The color of Trevor's turtleneck turns from black to gray, when he and Curtis go to the Dreaming Tree during the first day of work.
In the S&M club, although it's supposed to be taking place at night, you can see daylight seeping in through the closed curtains.
It's never explained how Jocilyn knows everything at the end of the game.