In the scene that Alex, Alvaro and Vando are smoking and drinking by the fire, the bottle that is left next to Alvaro when the other two are peeing moves from his left to his right between camera switches.
When Alex, Alvaro and Vando are smoking and drinking by the fire, you can see that Alex isn't actually smoking as no smoke comes out of her mouth. She doesn't even open her mouth after one of the puffs.
In the scene that Alex, Alvaro and Vando are smoking and drinking by the fire, Alex and Vando stay up to pee while the camera shows a quiet Alvaro. For a moment, you can still hear the sound of the liquid moving inside the bottle as if he was drinking, while the camera shows that he is sitting still and the bottle is on the ground.