Language development identified milestones that applied to children around the globe: all babbled around 6 months, said their first words at about 1 year. The development of language in children progresses from the prelinguistic vocalizations of crying, cooing and babbling to the use of complex, unique sentences. Crying is the first form of verbal expression and while it can be upsetting, it serves many useful functions. It conveys certain demands and needs of an infant. Cooing normally begins during the second month of life. Coos are articulated. Vowel-sounds that seem to occur during pleasurable or relaxed times for the baby, such as being held or rocked. Babbling, the next form of vocalizing begins at about 5-6 months. Like crying and cooing, it appears inborn but it can easily modified through attention. Smiling and imitation or other positive reinforcement to the babbling will increase it. Children develop competence in the production of phonemes during this time. Phonemes are the smallest part of language and the basic sounds of speech. At about 9-10 months, children learn to recognize and use the types of phonemes most often heard and drop foreign phonemes. Deaf children will often lapse into silence at the end of the first year, as they have no experience on which to base further language development. Infants understand many more words than they are able to express. They usually say their first words at approximately 11-12 months but they understand the meaning of bye bye, sleep now and time to eat long before they can say the words.