If you hear strange noises
I had a great Accounting lesson today. It was about Depreciation and our teacher brought a large purple toy car which she waved about excitedly while explaining the capitalized costs of new assets such as motor vehicles. Every now and again she would accidently set it off and it would starting playing a jaunty tune, that sounded suspiciously like "If you're happy and you know it, clap your hands!" It was rather surreal to be having Playschool flashbacks in that particular class.