Can i let my animal carry things for me on Shabbat in Reshut Harabim ?
If not, why does the talmud state in tractate
Pesachim daf 66 amud alef, , see rashi that when the
14 of Nissan was on Shabbat they placed the
knife on the animal to carry it and there was no problem
of shevisas behemto. Why not ?
You animal is not allowed to carry things for you on Shabbos, however in a backhanded way it is permitted. The gemora Shabbos 153b says that there is no prohibition for an animal to do something with a shinui, in a way that even for a person to do so, would only be a shvus. Therefore since the animal is carrying the knife in an awkward way, it is permitted, and this is what Rashi is saying.
Also see Magen Avrohom 305-6, M:Z 9, Kalkeles Shabbos Shvisas Bhemto 7.