Reference for Bava Kamma 39:4
והיכא איתמר דרבא אהא דאמר רבי אושעיא בהמה ברשות הרבים הלכה ואכלה פטורה עמדה ואכלה חייבת מאי שנא הלכה דאורחיה הוא עמדה נמי אורחיה הוא אמר רבא בקופצת
With reference to what was Raba's statement made? — [It was made] with reference to the following statement of R. Oshaia: In the case of an animal on public ground going along and consuming, there would be exemption, but if it was standing and consuming there would be liability to pay. Why this difference? If in the case of walking [there is exemption, since] it is usual with animal to do so, is it not also in the case of standing usual with it to do so? — [It was on this question that] Raba said: 'Standing' here implies jumping [which being unusual was therefore subject in the law of Horn].<span class="x" onmousemove="('comment',' Which could not be exempted from liability even on public ground. ');"><sup>1</sup></span>