That’s the thing: 5-Volt is actually asleep here. What you see here is her soul checking up on 9-Volt. If she catches you playing, her spirit summons her physical body and wakes her up in a rage.
i like to imagine she can very easily tell he's faking it but just keeps doing this anyway for fun. For example, at 13:11 she is LESS THAN A FOOT AWAY FROM HIS FACE. She's doing this on purpose.