Don't be obtuse.
Well, you start by asking this question
Based on Lucius' build, can he trap someone in the bag indefinitely?
which I answer
Not necessarily the best, certainly not the only, but here is one way.
Bag of Holding: (Total: 124 Active Cost, 27 Real Cost) Extra-Dimensional Movement (Related Group of Points in Time, Physical Location Same As Starting Location), Reduced Endurance (0 END; +1/2), Usable As Attack (+1 1/4) (124 Active Points); Conditional Power Only on objects that fit in the mouth of the bag (-1 1/2), Limited Power To send object forward to when it is removed from bag (-1), OIF (-1/2), Gestures (Requires both hands; -1/2) (Real Cost: 27)
Which at first you deny then acknowledge is an answer, then you ask another question
How does that look to the character using the bag (or the person that would be going in)?
Which I also answer
To one of them, it looks like their friend(?) with a bag pulled over their head. To the other, it looks like the inside of a bag. Probably dark.
You didn't ask what it sounds like, but I imagine it sounding like someone saying "Okay, why did you just pull a bag over my head?"
And now you accuse me of being obtuse, but you ask what amounts to a restatement of the same question I had just answered
What happens when someone tries to do this?
Which I suppose I could answer by saying that what happens is that one person pulls a bag over another's head and tugs down on it while the other person is standing there confused and unable to see. Or maybe one person is standing with feet in a bag and another is holding the bag's mouth at the first person's knees and tugging up on it. But if I actually answer any of your questions, I begin to suspect that will only lead to further questions, or the same ones over and over. So I will try to do as you suggest and stop being so obtuse as to remain trapped in your Bag of Questioning here. And I will try to remember to specify "Inanimate object" when that's what I mean in a Limitation or description.
The palindromedary says I actually DID answer that last question, and I guess I did. The Bag of Questioning is hard to escape!