You should see the disgusting stuff that accumulates inside computers. Never, never eat around your computer. There's nothing worse than taking a laptop apart to find more crumbs stuck inside the keyboard than a Saltine factory. Roach infestations smell particularly nasty.
They're like little vacuum cleaners. Especially if the person is a slob and smokes (a computer smelling like a overstuffed ashtray is usually jammed full of dust too).
I've picked a prosecutable quantity of a particular type of plant from a laptop keyboard, cumulatively probably a packet of cigarettes worth of tobacco in a year, stuff that's fairly clearly dried coke or similar, and other things probably best left unidentified.
Keyboard is probably worse than most public toilet seats.
