'Eurch' is also the sound a Centaur makes when speaking.
More of a screech, it's common phonetic notation is 'EURCH' - all in caps, with all but the 'E' and 'H' taking variable lengths.
EURCH spelled 'EURRCCH.'
EURCH spelled 'EURRRRRRRRCH!'
('I am not an animal.')
EURCH spelled 'EUUUURRRRRRCCCCCCCCCCCCH!!!'
("There's a fucking nail in my hoof!!!')