Question: Is it me, or does Medusa's head open her eyes as Perseus holds her head up after leaving the temple?
Answer: I watched this scene several times on YouTube. When Perseus walks out with the severed head, the eyes are closed. Just as Perseus raises it, Medusa's eyes suddenly appear to open. Zeus is then heard telling Perseus to "fulfil his destiny" amid the thunder and lightning. Her eyes are wide open at this point. I interpreted this as showing that Medusa's power still resides within the head, even though she is dead.
Answer: To me, it just looks like the way the prop catches the light as the actor lifts it up, and then higher up, the angle of the prop isn't catching the light in the same way.
Bishop73