What does 'rah-rah' mean?

What's "slack" mean? Does it mean similar to "loose?"

Yeah, that's right! It does mean "loose!" It's when something isn't too tight, or it means to give something extra length, so it isn't tight. Ex: Put some slack on the rope. Ex: The nets are slack, so the gymnasts won't get hurt when they land on them.

I thought "win" or "lost" is kinda like a result. But do you say "I'm winning/losing"? It sounds a bit awkward to me. Is it common to say like this?

Yes, it's very common! "I'm winning/losing" is used to express the current status of the competition/contest/match at that moment. It may not necessarily refer to the end result, but rather, what is happening at that moment in time. Ex: I'm winning! I think I'm gonna win this game! Ex: He's losing. I think we should cheer him on louder.

Does "took care" have the meaning of "something is resolved"?

'Take care of something' largely depends on the context at hand. In this context, to 'take care of something' means to 'handle' or 'solve' the situation, as in this case the "rat infestation". Ex. Did Jennie take care of the trash? It is also commonly used to take care of someone or something, you look after them and prevent them from being harmed or damaged. Ex: I have to take care of my aunt. It could also be used in a darker tone, as in 'to kill', 'eliminate', or 'exterminate'. Ex: The FBI tried several times over the years to take care of Castro, but failed.

What does "long face" mean?

Good question. "Why the long face" is an informal way of asking, "Why do you look upset?" Ex: Why the long face? Did something happen at the party last night? Ex: She had a long face when she saw her boyfriend with another woman.

Could you tell me how to use "flossin' "?

"Flossin'" is a slang term that refers to showing off something expensive that you own. Here, she says her "neck" is "flossin'" because she is referring to an expensive necklace that she is wearing. "Flossin'" is not a word that is used in conversational English. I do not recommend using this word because many native English speakers do not know what it means. Ex: I was flossin' my new watch yesterday.