We used to pray and animals would pass in front of us. We mentioned that to the Messenger of Allah (may Allah's peace and blessings be upon him) so he said: If anything, like the back of the saddle, is placed in front of anyone of you, then nothing that passes in front of him (but behind that thing) can harm him

Talhah ibn ‘Ubaydullāh (may Allah be pleased with him) informs us that they used to pray and that animals would pass in front of them. They mentioned that to the Messenger of Allah (may Allah's peace and blessings be upon him) so he told them that as long as there is something between the praying person and the passer-by, like the end of a saddle, then his passing will not harm him. Some of the benefits of the Sutrah are: maintaining the prayer, staying away from things that reduce its reward, repelling any guilt from the passer-by, and sparing him any difficulty or embarrassment.

صحيح مسلم، المحقق: محمد فؤاد عبد الباقي، الناشر: دار إحياء التراث العربي، بيروت. توضيح الأحكام من بلوغ المرام، لعبدالله بن عبد الرحمن البسام، مكتبة الأسدي، مكة ، ط الخامسة 1423هـ. منحة العلام في شرح بلوغ المرام، تأليف: عبد الله بن صالح الفوزان، ط 1، 1427هـ، دار ابن الجوزي.