Was it Puppy's Rule of Twelve?
http://www.uvhs.org/behavioral_docs/the_puppys_rules_of_twelve.pdfMy older puppy was well socialised (or so we thought!) but nobody ever thought to show him someone with their hands up their sleeves - he barks like mad if you 'disappear' your hands inside your sleeves, it's quite bizarre. And a little girl at dog training folded her legs up underneath her on the chair - that was scary too! Most dogs I know come and snuffle at your hands if you hide them, but not Tarn. He obviously doesn't like body parts disappearing!