Between the ages of one and two, toddlers seem to go from babbling hesitantly to confidently chatting up a storm. But how? Researchers have proposed that toddlers acquire a special function that enables this verbal explosion, such as syntactic bootstrapping (using a new word's context to determine its meaning). Bob McMurray of the University of Iowa devised a mathematical model to study the problem and found that tots inevitably experience a rapid increase in word learning after a set period. Initially little tykes can repeat only the most often heard words, but four months later they might command several hundred words that they hear only occasionally. This learning curve takes the shape of a simple, normal statistical distribution—a bell curve—and any child mastering language will travel along it. The curve may also explain why some children learn language faster than others: they might have been exposed to more words or have better short-term memory.