Scrapie
The name scrapie is derived from one of the clinical signs of the condition, wherein affected animals will compulsively scrape off their fleeces against rocks, trees, or fences. The disease apparently causes an itching sensation in the animals. Other clinical signs include excessive lip smacking, altered gaits, and convulsive collapse.
Plop: The Hairless Elbonian
Plop was so named because, according to Adams, that was "the first thing my mom heard when I was born three months prematurely." From strip #21, Plop starts to rename himself "Squat", after his name certificate misspells "Scott". The background reasons for this name-change are explained in "Dilbert newsletter" No. 39