Lactnuts -
I'm not quite sure what is meant by "curling" the tongue.  If it means
bringing the sides up to form a tube, that is called "rolling the tongue".
It's an inherited trait.
Just in case anybody is actually interested, it's estimated that only 30% of
the population can roll their tongues.  My father could, my mother can't.  My
three sisters and I can.  My husband cannot.  Two of my children can, the
other two cannot.
As an interesting side note: at a Ripley's Believe It or Not museum they had
information about rolling the tongue and invited people to look in the mirror
and try it.  Later on in the museum you could look through the *mirror* from
the other side and see all the people trying to roll their tongues.  :-)
Anyway, I seriously doubt rolling one's tongue as anything to do with the
ability to breastfeed.
Cynthia D. Payne
LLL of Berkshire County Massachusetts