mouse nipples

[Jules Richardson]

The mouse cursor on this laptop (an aging Thinkpad) keeps on moving by 
itself - presumably the hardware side of it's the same on all laptops 
with a mouse nipple though. Anyone know if it's worth me trying to get 
underneath the keyboard to fix it (I assume it's a dirt-related problem) 
or is the problem more likely to be some sort of obscure software issue?

(I have no idea when mouse nipples first appeared on laptops, but I 
imagine they're on topic just :-)

cheers

Jules