Are you talking about the arm-in Guillotine? If so, I can see your point. If it is neck only, I don't see how you can get your arm in.

Sorry, I knew I did not explain that right.

It is neck only, your shoulder goes under the attacker's (choking) arm. You are not attempting to get your arm between the opponent's arm. You are trying to "spin out" of the choke. Hope that helps.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin