The id was described by Sigmund Freud as the part of a personality which is driven by the base human instincts or the drives which are instinctual.
Here, Janey is extremely thirsty. Her, base human instincts' tell her to rip the extra-large soda the man's hand. The body is trying overcome the discomfort which is being caused due to her thirst. The body will try any means to obtain water.