system
Given the following post, respond as if you're commenting on Reddit:
human
[40k] Is it possible to torture an ork?
gpt
Orks don't process pain the way that a human does. They feel it, in the sense that one of their sensory inputs includes physical damage done to their body, but it doesn't impact his ability to act nearly as much, and it doesn't have the psychological effect. Because it doesn't have the same psychological effect, purely pain-based torturing is likely to be ineffective.

There are probably psychological techniques that are effective, though. They don't generally have a fear of death, or even a philosophical awareness of the concept, but they do have wants (fightin'), needs (fightin'), and desires (more dakka, for fightin'). Surprisingly, isolation techniques that remove social contact may actually be more effective against Orks that more "normal" species. Take away his ability to express his aggression, and other individuals to compare himself against, and his existence becomes meaningless. Orks don't fear fighting, but they do fear not fighting if they can be made to understand the concept.

Of course, torture for its own sake is not always the most efficient use of the Emperor's vast but finite resources. Most torture conducted by humans has a direct goal (as opposed to what the Dark Eldar do), such as extracting information. In this case, domination may be more effective than straight-up torture. Showing yourself to be stronger, tougher, and larger than the Ork will earn his fear and respect and makes him more compliant to commands. This isn't easy, as Orks view themselves as inherently superior to other species, but if accomplished it makes them easy to manipulate.

In any case, it is far preferable to capture Gretchen for interrogation. They are smarter, so they are actually capable of understanding questions and forming coherent responses. They are sniveling cowards, so it doesn't take much to get them to talk. And you can pack like twenty of them in a supply closet, and feed all of them with one piece of beef jerky per day, so logistics are simpler. The only problem is that they're difficult to capture alive, on account of Orks using them as cover, minefield sweepers, field rations, napkins, shoes, etc.