Howard presses his lips together, tempted to refuse to do anything until he gets a little bit more of an explanation from the Doctor, but he decides he's seen enough to have a general idea of how this works. Somehow, the crystal responds to people's energy or something. Dim is bad, bright is good. Simple enough concept.

Not that it would have killed the Doctor to say any of that out loud, but whatever.

He reaches a hand out and ever so gently touches it. It glows, more brightly even than when it had just popped out. He pulls his hand away, then puts it back, making note of how close he has to get to it to reach maximum brightness.

"So this is what, a mental link to steer the ship? And whoever had it last decided it was an awesome idea to slam it into a wall?"