Rein (noun) : a strap fastened to a bit by which a rider or driver controls an animal —usually used in plural
The Shawl by Louise Erdrich
“As the uncle slapped the reins and the horse lurched forward, the boy tried to jump into the wagon, but his mother pried his hands off the boards, crying, Gego, gego, and he fell down hard.”
This statement explains that the wife, Aanakwad falls in love with other man and after giving birth to his child, she tries to run away from her home and she leaves her son behind as she takes her daughter and newborn baby with her on the wagon.