Mind control that doesn't go away. Sure, they're out of Whumper's hands, but for whatever reason, the control doesn't lessen entirely.
It's not noticeable at first, but something is undeniably happening.
Their face will go blank sometimes, and they'll snap to attention.
They only speak when spoken to, and even then, they're much too quiet.
Offhand comments are followed to the letter, they let themself be touched and handled and do whatever they're told, no complaints.
When (if) their team figures this out, it complicates things. They can't be as casual around them as they'd like to be, have to monitor everything they say to make sure they don't take advantage of Whumpee.
Carefully phrasing questions to make sure they aren't misunderstood as orders, always leaving comments open for questions or objections... the vulnerability of caring about someone who can't consent to... anything, right now. Even the seemingly normal things.