Question: How should a GM role-play a torture scene for a PC?

In one of my games, one of my PCs will be captured by the enemy who wishes to get information from him, using... less than ethical methods.

Leaving whether or not the information is divulged to a dice throw seems a waste, but on the other hand, it's hard to force a player to give up info if he doesn't want to.

I'm playing an L5R campaign, with the L5R system.

Answer: 
And just for completeness sake, as nearly all answers here seem to address to the question "How can I avoid explicit torture scenes as a DM?"

If it is OK
===========

So after going through the metagame topic of "Is it OK?" (preferrably in advance), and if it is OK, you can role-play it in a nasty simulationist fashion.

Prepare for the session as usual: 

* [research the topic](https://skeptics.stackexchange.com/questions/4498/does-torture-work-well-as-an-interrogation-technique)
* print out some torture devices (in black and white) and maybe some mutilated human bodies
* play out the two concurrent processes of torture - the dialogue with the NPC, and enduring the actions of the NPC (torturer)
* don't start out by "I'll ask nicely", start with some pain in order to put the subject in a stressed state, where lying would be detectable
* tortured subjects usually get executed afterwords, if they hold no more information of interrest

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Leave the system at the background
==================================

> 
> but on the other hand, it's hard to force a player to give up info if he doesn't want to.
> 
> 
> 

```
- Just hold still while I am doing to you eye what just happened to your finger. 

```

This situation is intended to scare **both** the character and the player. The character ... well, this is clear. The player, because he/she knows that you, as a GM, stand up to what you declare, and his character is going to have that -5 on any ranged check ... forever (in a non-magic setting). 

*"Hold Still, I don't have good depth perception!"*

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How to establish credibility
============================

Needless to say, however, don't mention the ranged penalty during role-playing the scene. "You will get -5 to ranged attacks, are you sure you don't tell him the truth". This kind of metagaming brakes immersion! **Role**-play, then, as an epilogue to the scene, summarize the mechanical repercussions of the scene. Doing this several times in different situations immediately establishes the "you, as a GM, stand up to what you declare", mentioned above. 

Of course, do this for beneficial scenes too: "That kiss from the elven princess boosts +1 permanent Dex bonus. And now for the chase scene."
I suggest the following: make it a part of the narrative. Make the character get hurt. Inflict some damage on him, use insanity rules if your game has them. Get into the character's psyche. Tell the player that if he doesn't comply, he'll get hurt. A lot.