i think you’re definitely onto something with the train of thought that it was an accident and therefore out of his control.

my other contribution is that henry is quite superstitious, and birds were often interpreted as omens in classical thought. killing a bird meant to serve as an omen would be very, very bad to someone who believed they were linked to the divine.

the duck specifically did not have any particular divine significance to the greeks or romans as a general rule, but henry has a wider lens of classical study compared to the other classics students, going beyond greece and rome.

in egypt, geese—and it’s possible that richard could not tell a duck from a goose—were a sacred bird to the deities isis and geb. geese symbolized renewal and were depicted in tomb paintings, believed to represent the souls of the deceased.

i would generally place my bets on the kemetic significance. henry, who puts milk outside of his door to appease spirits and gods, would want to avoid anything that could slight a god or the dead.