No preparations whatsoever! - But if you know the trick, you can get out of it very easily!
> See also the (unfortunately out of print) Felix Farell book The "F-Files"
The thumb cuffs are not prepared , so they can be examined thoroughly without any problem.
To open the clamp, the key must first be turned/pressed to one side and for the second bracket to the other side.
It is therefore impossible to free yourself from the thumbcuff if both thumbs are locked, even if the key is in the lock.
Demonstrate this with a spectator. Leave the key in the lock. They won't be able to free themselves. This can be expanded into a quite entertaining (comedy) sequence.
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