"Um, Jack," Jo called to him before he could go too far. She'd looked up and had a suspicion she'd found the psychic energy he'd mentioned earlier. "Does psychic energy ever look like..." she paused because her next words would be 'someone I subconsciously want to see' and that wasn't quite something she wanted to reveal to Jack. So instead she said, "A person." Although it looked the Doctor and he looked just the way she remembered, he was see-through and she knew it wasn't him.