 A delay in the phonological development of one or both twins (or two siblings at similar age of language development) is said to be a main cause of cryptophasia.Twins can develop the ability to communicate with one another without working within the grammar of their parents' language, thus possibly leading to a short-term delay in linguistic development of one or both twins.The causes seem largely not to be in the greater pre- and perinatal biological problems twins may experience, but rather in postnatal factors.