ass, donkey
馿 centers on a donkey or ass, a specific equine animal. The meanings are straightforward and refer to the same creature.
馿 combines 馬 (horse) with 户, which likely contributes a phonetic element. The character is used for donkey, an animal related to horses.
A horse 馬 beside a door 户: imagine a stubborn donkey blocking the stable door, refusing to move.
For ロ, picture a low donkey braying loudly: low -> ロ, and the donkey's sound echoes through the stable.