@marcyvq
To lower their guards probably? Getting them to lower their guards and completely believe he is now harmless. It will be easier to take action that way.
Further more, it is required for him to get the drug resistance skill. Don't wanna get drugged the third time yeah? And he will learn more skill.
In addition to that, Freya has already decided to drug him from the beginning so there are no other choices.
And yeah, he is a weakling at start so... he of course couldn't endure that much of pain. Fainting would be inevitable.
The only way to prove this theory of mine wrong is to cut somebody arm and don't let them faint. (On their own of course. If the medical team is there then there will be too much advantage. There is no medical team in the middle age.)