Humans can perceive the number of members in a small set without actually counting them or mentally breaking them into subsets; the upper limit of this ability is estimated at between 5 and 9 units, and this seems to hold true in sequences of audible stimuli (e.g. syllables in a line of verse);Scott 1993; Gasparov 1996, p 8. so it is no surprise that syllabic hemistichs tend to be very short (typically 4 to 8 syllables), and to be grouped — and therefore separated from their neighbors — by markers such as stress, word boundary, and rhyme.
