can you explain the parts marked with [(number) ... ]?

(Leonard exits down stairs. A moment later, Penny peeks out of her apartment, checks the coast is clear, and crosses the hall to the guys apartment. Knocks.)
Sheldon: (answering) Hello Penny. Leonard just left.
Penny: I know. I want to talk to you.
Sheldon: What would we talk about? We've no overlapping areas of interest I'm aware of, and you know I don't care for chit-chat.
Penny: Okay, can you just let me in.
Sheldon: Well alright, but I don't see this as [(1) a promising endeavour.]
Penny: Okay, here's the deal, we are going to throw Leonard a kick-ass surprise party for his birthday on Saturday.
Sheldon: I hardly think so, Leonard made it very clear he doesn't want a party.
Howard: Did someone say party?
Penny: He just doesn't know he wants one because he's never had one.
Howard: I suppose that's possible, but for the record, I've never had a threesome and yet I still know I want one.
Penny: Howard, here's the difference. The possibility exists that Leonard could have a birthday party [(2) before hell freezes over.]