HAHA Andy,
Its called a barber chair because the tree mimics the motion of a barber chair.. While the top of the chair goes forward and down, the legs go back and up... When a tree barber chairs, the forward force on the top, exerts a force on the base of the tree that splits the trunk along its grain, so the front half (or thereabouts) of the trunk (above the notch) stays put, while the back half splits and lifts, hinging on the stationary front half. I've heard of trees hinging at 40', which would mean a 40' split in half trunk flies back as it lifts to a 40' height, and then can break at the unintentionally high hinge, and come falling down 40' to the ground, and landing 40' behind the stump... That is why the escape route should be 45 degrees back, not straight back.. Barber chairs will happen anytime the forward pulling force on the trunk is great enough to split the grain of the trunk, but not great enough to trigger the hinge to fold.. This is most often caused by heavy front leaner on species that split grain very easily, like ash, or can be caused by an unintentional bypass of the two face cuts, called a "dutchman" as was the case in the video, and can also be caused by pulling on the pull line too early in the backcut, before the hinge is formed.... this is one of the very real dangers of pulling with a truck or machine.. If you don't know what you are doing and call for the pull too early, you can barber chair the tree or break out the top.
I talked to one contract climber that said the guy that hired him pulled early when he was cutting a mulberry and you would not have believed anyone could have crawl out from under the top of that tree unhurt... He got lucky.. then ended up breaking his back or neck in a car accident... you just never know..