"Brain" as Slang for "Oral Sex": fun with metonymy

[Arnold M. Zwicky]

On Nov 6, 2004, at 1:06 AM, Grant Barrett wrote:

> Two more data points: "hanging brains" is to dangle one's scrotum
> through the fly of one's pants and "to brain" someone is to hang one's
> scrotum next to or on the face or head of a sleeping person, usually so
> a picture can be taken.

fascinating.  ya learn something new every day around here.

what's the motivation for "brains" 'scrotum'?  is it based on the
expression "have balls for brains" '[of a man] think with one's
genitals'?  or on a perceived physical similarity between a testicle
and a brain?  or what?

in any case, i'm interested in the expression, for a rather odd reason.
  in another part of my life, i'm a collagist, working mostly with
images of the male body and of gay love and sex; "They All Laughed When
the Hot-Hot Man-Man Sex Started: XXX-rated homoerotic comic collages by
Arnold Zwicky" was part of a local group show in may of 2003.  (it
started years ago as a kind of art therapy.  now it's a semi-pro
hobby.)  i'm currently working on a long-range project on the ways male
models and actors (in porn and in the mass media) display their bodies.
  so i've been collecting images in a large number of categories -- the
very common "pits 'n' tits" presentation, with armpits and nipples
vulnerably displayed, for example.
one of the categories i call "peekaboo"; this is where a guy's
equipment sort of spills out of his confining clothing.  there are many
subtypes of the peekaboo display, among them the through-the-fly
escapee (which tends to look really silly, probably because it's the
classic flasher pose).

but -- yes, i do have a point here -- i have yet to collect a pure
"hanging brains" display.  plenty of scrota proudly presented, but
always with an accompanying penis, which takes center stage, so to
speak.  probably there's a specialist corner of the sexual world where
scrota are celebrated entirely in their own right, but i haven't yet
come across it.  (lord knows, the variety of sexual tastes and
fantasies is astonishing.)

arnold, your friendly neighborhood pornographer