Claire: Luke, come say good-bye to your sister.
Luke: [muffled voice] I'm right here. Bye, Haley. Have fun. Don't drink too much beer and shots of Tequila.
Haley: Why are you wearing that mask?
Luke: Uh, I like it.
Claire: He doesn't want you to see him cry.
Alex: He's literally masking his emotions.
Luke: No!
Haley: That's so sweet. Come here.
Luke: It's not sweet. I'm an evil cyborg. Half my face was burned off in an industrial accident, and the mask is hiding the servos that control my mouth.