I love the RNC choke where they trap your arms under their legs. It makes you completely helpless. I like it best when they apply the choke gently/slowly and talk to you while applying it.
An example of the hold is at the 2:15 mark in this video:
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I ask for this hold in most sessions. I much prefer it to the regular RNC as, as far as I know, it is impossible to defend against once your arms have been trapped properly.