[@Chrononaut]

 There were actually two measures, one being the oil and the second being a steel bar that seperated the hands a distance apart like true manacles. Realistically, I would imagine any dark elf having the Ancient Ancestor ability would be maintained in such a manner. Otherwise, they'd require prior knowledge to ensure things of that nature. Subsequently, with spells that may influence intelligent beings I couldn't say. The only thing I know for sure is that in the game without proper leveling in illusion, casting  spells like fury or fear aren't very useful once you start encountering enemies when in your 20 and 30 levels. So depending on the caster, it may not be an issue. I would presume that if the mage was a notably high level caster that information would have been obtained well before they finally went after the person.