Bonsoir, Il va faire mal à ma meilleure amie. He's going to hurt my best friend. (physically) Il va faire du mal à ma meilleure amie. He's going to hurt my best friend. (emotionally) This is an excellent question because given the two examples above, sans the state in parentheses it would be very difficult to differentiate a translation; however, also in the lesson it states that «faire du mal à» is specific to emotional or psychological pain, hurt while «faire mal à» is specific to a physical hurt, i.e. cut, bruised, kicked, etc. Votre question m'a plu certainement parce qu'il m'a fallu penser. Merci beaucoup ! Bon travail! J'espère que ma réponse vous aidera.