What would happen if someone tried to cast the imperius on a wizard who is already under the imperius curse?

I imagine that one of four things might happen:

1. The attempt fails because the victim is already under someone else's control. This might happen because

• the imperius curse can't override itself (or cancel itself out) regardless of the caster.
• the wizard attempting to cast the imperius curse is weaker than successful caster or the wizard cast a bad imperius (one that wasn't cast properly and wouldn't have worked even if the victim wasn't already under someone else's control).
• It's impossible for two people to have control over someone's free will at the same time.
• It's impossible for someone to be under the full control of two wizards at the same time

2. The attempt would be successful and override the other imperius curse. This might happen because

• the imperius curse can override itself
• the outcome is dependent on the skill of the wizard casting. e.g.: an imperius cast by Voldemort would override one cast by Arthur Wealsey, while the reverse would not happen.
• If it's not dependent on the strength of the caster then all that matters is that the curse is cast properly
• it's impossible for two people to have control over someone's free will at the same time
• It's impossible for someone to be under the full control of two wizards at the same time
• *Would the original caster be aware that the curse is broken?

3a. The two curses cancel each other out and the victim is free. This might happen because

• The imperius can't override itself and instead cancels itself out
• it's impossible for two people to have control over someone's free will at the same time
• the effect is not dependent on the skill of either caster, instead on the spell being cast (a mind/body control spell)
• It's impossible for two people to have control over someone's free will at the same time.
• It's impossible for someone to be under the full control of two wizards at the same time.
• *Would the original caster be aware that the curse is broken?

3b. The two curses cancel each other out and the victim's mind is severely harmed (like Crouch sr.). This might happen because:

• The human mind can't handle being under 2 imperius curses at once and any attempt at putting someone under 2 imperius curses will result in severe and irreversible damage to the victim's mind.
• The imperius can't override itself and instead cancels itself out
• it's impossible for two people to have control over someone's free will at the same time
• the effect is not dependent on the skill of either caster, instead on the spell being cast (a mind/body control spell)
• It's impossible for two people to have control over someone's free will at the same time.
• It's impossible for someone to be under the full control of two wizards at the same time
• *Would the original caster be aware that the curse is broken?

I was wondering because I know that during the first Voldemort war there was fear that anyone could be under the imperius curse. I figure that if 1 could happen then wizarding families would all cast the imperius on each other to keep themselves safe from a death eater's imperius. If 3a or 2 could happen then families of wizards would just cast the imperius on each other to prevent a DE's attempt to cast it on them would fail or to break previously cast imperius curses.

I think 3b is the most plausible because it explains why people weren't protecting themselves from the imperius by casting it on each other.

I was wondering what other people's thoughts on this were. I apologize in advance if this question has already been asked or was answered in canon.

 

Considering HP 3b is the most likely

 

Version 4:

The Imperius seems to work in two modes- active control and passive subjugation. When Harry was being commanded by Crouching Moody to jump, it was active control. Rosemerta and Katie were in passive subjugation, following the instructions that Draco had given them. Any casting starts in active mode, during which the victim can try to fight off the curse. Once fully in control, the active mode shifts to passive whenever the victim is left idle.

If another person casts an Imperio on someone in passive mode, the victim would fall under the active casters thrall unless told to do something that ran contrary to previous instructions. Assuming the instructions couldn't both be followed, the spells would be fighting for influence in the victim's mind. Regardless of which caster won, the victim would have been double-doped on happy control vibes, which might just send them into a coma.

A second caster trying to influence someone already being actively controlled would initiate the power struggle in the victim's mind immediately. Strongest will wins, but if the casters are near-equal it might take a while to settle the fight, leading to possible lobotomy.

I have this notion that, since the Imperius uses pleasure to induce control, the 'right' way to break someone out of the Imperius is with pain- specifically the Cruciatus.

Why didn't citizen wizards and witches try to place each other under the Imperius to offset possible ambushes? Probably because it's a capital crime with an automatic sentence of life in Azkaban. Same thing with the Cruciatus. Besides which, the only people nutty enough to experiment on other people to figure this out would be Voldemort's crew or the Department of Mysteries- in both cases, I'd say Rookwood was the researcher.

 

There's another possibility: both curses are successful and the person is torn apart (in some cases literally) by trying to simultaneously obey contradicting commands.

 

"I'm the little voice in your head."

"No, I'm the little voice in your head!"

"I'm the little voice in his head!"

"No, I'm the little voice in his head!"

Just another day in the life of the doubly-imperiused.