Berachos 33a

Gemara: "There was a story about a place that had an ערוד..." Look in Rashi for the definition. However, on 9b Rashi says that ערוד is a wild donkey. Perhaps the answer can be based on a gemara in Chullin 127a, that is clearly talking about the same ערוד as our gemara is, and the Shitta Mekubetzes (on the page), note 3 says to pronounce it "arvad." So, an arod is a wild donkey, and an arvad is the animal that bit R' Chanina ben Dosa in our gemara, although the spelling is the same.