Game was in his mouth. That Esau would honor his father and whatever he would hunt, his father would eat it. Another interpretation: Game was in his mouth. That he would ask his father how to tithe salt and straw, and Isaac loved him because he thought Esau was very stringent about the mitzvot. But Esau only asked those things in order to deceive his father. But Rebecca saw Esau's wickedness and she did not love him, but she saw that Jacob was a mild man who loved to learn Torah and who would go to the study hall, and so she loved him.