What did George do once that made him stop playing jokes on Lennie was

Answer: George told Lennie to jump into the river even though he knew that Lennie could not swim

Explanation: George told Lennie to jump into the river even though he knew that Lennie could not swim. Lennie does jump but nearly drowns. Lennie is so grateful for being saved that forgets that George had told him to jump in the first place. Consequently, George decided to stop playing jokes on Lennie.