Why didn't the Thin Man nod his head...

When Vivian, revealing her gun to Dylan the moment Knox reveals to her that he is the real enemy, says that Dylan's "girlfriends" are dead, just as the Thin Man comes in. Vivian turns to the Thin Man, asking "And Corwin?" I know the Thin Man is supposed to be mute, but if he can laugh at the end of the movie when he pulls off Alex's hair like he did to Dylan, he should be able to give Vivian a nod. And we saw him kill Corwin, of course.
By the way, I think it was a really shocking twist that Eric Knox turned out to be the villain, but it is overshadowed by the star power. And I'm pretty sure Full Throttle had an inferior plot to this one, even though I didn't see the 2nd.