Thank you for a most interesting question. I will answer it as it is
asked, in two parts.
A. What is the stuff that gets stuck inside mice?
Particle matter in the air - 'house dust' as it is usually referred
to, is what gets into mice. The mouse pad (or any other surface you
use to move the mouse on) is open to air most of the time, thus
allowing a surface for house dust to settle on. With the movement of
the rubberized tracking ball which is in the well at the bottom of the
mouse, this dust collects on its surface. Over time and repeated
movements, the dust gets trapped between the rubberized ball and the
three plastic sensing wheels inside the well.
The moisture in the air and from your fingers or part of your palm
which is in contact with the surface (mouse pad), along with the
warmth of your hand condenses this dust material into physically
compressed masses. This mass gets sticky with time and lodges itself
well on to the plastic sensing wheels and the rubberized ball.
The ball is rubberized so that it becomes frictional, so as to
maintain regular and smooth contact with the surface. The surface
(mouse pad) itself is also made frictional for the same reason.
(This is required, since the rotary movement of the ball, wheels,
etc., have to eventually get converted into linear and precise
movement of the arrow on your screen. There is an
electrical/electronic process involved, which is out of this
In effect, you have a couple of surfaces that contain enough pitting
for the dust particles to get ensconced within. Gradually, with
humidity and moisture, this dust gets sticky enough to grow large
and get flattened between the rubberized ball and the three plastic
sensor wheels. It finally ends up on the sensor wheels and impedes
smooth movement. (This results in skipping or erratic movement of
the arrow on your screen.)
B. and what's it called?
NOUN: 1. Slang a. A coating or an incrustation of filth or refuse. b.
Something loathsome, despicable, or worthless. c. One who is
contemptible or disgusting. 2. A disease or ailment, imaginary or
real, especially one affecting the skin. 3. Sports Heavy, sticky snow
that is unsuitable for skiing.
ETYMOLOGY: Middle English crudde, possibly from Old English *cruden,
past participle of crdan, to press, drive.
[ http://www.bartleby.com/61/45/C0774500.html ]
The American Heritage® Dictionary of the English Language, Fourth
Edition. Copyright © 2000 by Houghton Mifflin Company.
NOUN: Slang. Foul or dirty matter: dirt, filth, grime, muck. See
Rogets II: The New Thesaurus, Third Edition. Copyright © 1995 by
Houghton Mifflin Company.
As you can see, the term crud that you used to describe this mass of
compressed house dust is very apt, when you consider A coating or an
incrustation of filth or refuse from the above!
dirt, grime, filth or muck as also apt for describing what we
have on hand.