Why can’t the man tell the woman what the present is?

W: I don’t see why you drive me here, Robert.
M: Oh, I may need some help from you.
W: I’m just curious why you need my help to pick up a birthday present for Ava. Must be a big gift?
M: Yeah, pretty big.
W: Well, what is it?
M: Sarah, [8C]I shouldn’t tell you yet. It’s a surprise. Well, unless you promise to do me a little favor.
W: What kind of favor?
M: [8C]Keep the present at your apartment until the party.
W: What’s the matter? Why can’t you keep it at your apartment?
M: I don’t think I could hide it from Ava.
W: Why? What in the world is it, Robert?
M: Here we are. Sarah, can’t you do me this little favor? It’s only for a couple of days, after all. I promise it won’t cause you any trouble or cost you any money.
W: Robert, why do we slop here anyway? There are no department stores on this block. Wait a minute…It’s that pet store over there, isn’t it? You’re going to buy a tortoise or a gorilla or something for Ava’s birthday, and you want me to keep it, right?
M: It’s not a gorilla, Sarah. It’s just a little dog.
W: Sorry, I can’t keep pets at my apartment. And I hate dogs.
M: Well, it’s not your pet. And you’ll love this dog. He’s a sweet little puppy. Only eleven weeks old. How can I keep him at our place?
W: All right, all right, I’ll do it. I’ll put up with it. Just stop telling me again that it’s a "sweet little puppy".
And you provide the dog food, all right?
M: All right.