Based on the information provided within the question it can be said that in this scenario Terri Schiavo would only be able to Groan and move her eyes. This is due to the fact that the brain stem controls vital functions that include eye movement, breathing, digestion, heartbeat, and even swallowing, as well as sending information to the rest of the body. But if the only thing still functioning is the brain-stem then those signals are rendered mute and only the main functions of the brain-stem will be working allowing her to groan and move her eyes.
