Yeah.

[ He did. John frowns uneasily at the scar, at Ianto's fingers tracing it, and a nerves begin to bubble uncomfortably through him again. ]

This guy was... keeping one in a cell, keeping it starved then letting it feed on people in bursts. Stopping it just sort of killing them. Turns out the wraith didn't like it much either, helped me escape once he was... strong enough.

[ From... feeding on him. ]

Then he, uh, undid it.

[ ... Which is, apparently, possible...? ]