How did Hoid hurt himself in WoR interlude 7?

[Fabien]

During my reread of SA, I noticed in this interlude the guy who talks to Dalinar says Hoid hit himself with a rock several times. Hoid can't cause physical pain to anyone, inlcuding himself. So how did he hurt himself? The only thing I can think of is if he just pretended to hit himself with the rock but the dialogue about needing to know what the guy's company is in comparison to the rock doesn't really make sense then. Does anyone have an answer?

[RedBlue]

I think Wit’s antics in that scene were an elaborate insult/joke. His point was that the other guy’s company was comparable to getting hit on the head with a rock (ie, really bad). He’s doing it to entertain himself, not because he’s actually trying to achieve something.

We don’t know very much about Wit’s apparent inability to physically harm people. Either hitting himself on the head with a rock doesn’t count, or it involved more theatrics than actual hitting. 

[Weltall]

Presumably it's about Intent. Hoid can't intentionally cause harm to himself but he's perfectly capable of provoking someone else to harm him knowing full well what will happen. Brandon has also said that there's a Cognitive aspect to Hoid's inability to eat meat, which is related to his 'no harm' deal. By extension, if Hoid is putting on a show and isn't actually hurting himself (and knows he won't really be hurt) it probably won't trigger the whole 'becomes debilitatingly nauseous' thing.