I'm Glad That I'm Good for Something, I Guess

[via phone]
My sister: Hi, Eli7, I have a really important question for you.
Me: OK
My sister: In "Twin Towers," is "twin" an adjective?
Me: It's part of the proper noun.

[via e-mail]
Friend: Random question: I assume that you give someone a "heads up" not a "head's up" or a "heads' up"...
Me: Heads-up.