Yes, we wouldn't want you or anyone in the vicinity to have the life sucked out of you. That usually isn't good way to maintain friendships. [And he knew for a fact that such an ability tended to panic people as their brains couldn't comprehend. The terror sometimes killed them all before he was finished draining the life from them. It wasn't a fate he wanted Vira to have.]

When there is opportunity and after discussing the plan of action before trying.