I personally think it was a friendly discussion about the ad in the Austin newspaper. The hand on the wrist could also be interpreted as a friendly gesture that would precede a firm request to “knock it off”.
Paul does not look intimidated and I think that is the story behind the picture.
Ron Paul looks surprised and Perry looks pissed. Ron Paul isn't an easy guy to intimidate, so I wouldn't use that as a gauge.
Perry again looks furious at Ron Paul. Ron Paul is laughing and Huntsman is leaning away from Perry and toward Ron Paul. Paul is not intimidated, but Perry is puffed up like a gorilla trying hard to be intimidating.
Bad form.