it took me awhile to figure out what was a mantra cry and what wasn't, especially since every child's cry is different!!
with lindsay, her mantra cry is at the same pitch, fairly quiet, and usually doesn't last for more than 15 minutes. if it gets louder at ANY point, i know that she has moved from being able to self-soothe to needing my help. and believe me, you learn the difference very quickly between the types of cries.
one night, i was listening to her mantra cry and DH, who isn't quite as versed in the ways of BWing, was getting upset so i went into her room (against my better judgement). well, as soon as i put my hand on her back it made things worse, so i knew that i had disturbed the normal course of her putting herself to sleep. i quietly walked out of the room and within five minutes she has put herself back to sleep.
the danger with not recognizing a mantra cry is then the baby doesn't learn to put themselves to sleep as mummy or daddy is always "rescuing" them. babies are perfectly capable of putting themselves to sleep if we don't rush in at every little sound. as a first time mum, it took me awhile to get this through my head as i would rush in a the slightest sound. most of the time she had already rolled over and gone back to sleep and she was just fine! once i relaxed about it all and actually started listening to the cry, life got easier for both of us!