USA Today on "sucks "

[sagehen]

Larry writes:
>......  (e.g. the much-cited
"sucks eggs", "suck the hind teat", "suck wind", "suck (one's)
thumb")? ......<
~~~~~~~~~~
There used to be an expression -- haven't heard it in fifty years --
"teaching your grandmother to suck eggs"  (or variations on the same
image), meaning presuming to teach someone, who knows how better than you,
to do sthg. But why "suck eggs"?
AM