JokesMarriage Little Johnny’s Preschool Class Went On A Field Trip This Is Hilarious. Little Johnny’s preschool class went on a field trip to the fire station: The firefighter giving the presentation held up a smoke detector and asked the class….. “Does anyone know what this is?” Little Johnny’s hand shot up and the firefighter called on him. Little Johnny replied…. “That’s how Mummy knows supper is ready! See more Previous joke A Wife Asked Her Husband To Describe Her. Next joke An Elderly Man Goes To The Doctor.