Lara's mouth is dry, and she realizes that she hasn't had anything to drink all morning. The water level in her cells has dropped, and she feels thirsty. Seeing her classmates drinking from their water bottles is distracting her from paying attention in class, and, at the next opportunity, she will go to the water fountain and take an extra-large drink. Her feeling thirsty and taking an extra-large drink can be understood in terms of theory.