Why did Moshe refer to the animals that were in the field?
Rashi (on Pasuk 10) and Seforno (Pasuk 20) 1 : The decree was indeed confined to the animals that were in the field, and the G-d-fearing among them took his animals into the house.
Ramban: He mentioned fields because that is where most of the animals were kept. In fact, also those in the houses died as well. 2