The correct answer to this open question is the following.
The answer is "the eyes."
This is a traditional riddle in some South American countries. Whatever action is happening, when you are sleeping on your bed, the first thing you open is your eyes.
Spanish:
Nos estamos refiriendo a un tradicional acertijo sudamericano. Cuando estás dormido, independientemente de lo que esté sucediendo en otras partes, lo primero que abres son<u> los ojos</u>, y después, todo lo demás.