Most toddlers speak gibberish, uttering an easy new word here and there, before exploding into little chatterboxes seemingly overnight. Now researchers think they know why. It’s the “word spurt” effect, according to an intriguing new study conducted at the University of Iowa and published in the journal Science. Lead researcher Bob McMurray, a psychology professor, says the sudden vocabulary growth owes to the child’s need to decipher many words at once — some of them far more difficult than others. He says that, as long as toddlers are exposed to more difficult words than easy ones, the word spurt is “guaranteed.”