Basically educational:

We read with the daughter "Three in the boat, not counting the dog".
I am in English, she is in Russian.
As it turned out later, the phrase "stupid ass" was translated into Russian as "sweet ass".
But the more stunned Google translator, the daughter did not see well.

In fact, the first meaning of the word ass is a donkey. Which has ears. Moreover, in Jerome's time it was the only meaning in the written language; the meaning of "Jop" appeared much later. So the translation is correct.