Discorde: Hi, I think we both agree that a) throttle closure resulted in a yaw to port and b) that your Coriolis Effect also applies but I was trying to get to the source of the yaw swing in the first place as described by Scotbill.
I think it is difficult to argue that the rudder was always acting "in a free stream airflow" when every power change needed a rudder/rudder trim input! Thus for every given thrust there was a compensating rudder position. Removing the aerodynamic balance suddenly with the props blanking much of the airflow removes the initial required rudder moment hence the swing (my quote) Remember how on take-off with full power and slow speed left nosewheel tiller was required because of the rotational airflow on the fin until the rudder became effective.