Thanks Peachey and Nanren, it is algebra, and it is used to denote the initial state, at first I thought she was saying "U oh", but then I noticed she always pronounce the zero by starting with an "n" sound, like "no", so, based on Comandante and Peachey, i think it should be nought. :)

haha that's an interesting question, I have never thought about it before, generally I would use "脸" to refer to "face", while other words might have different meanings and their own usages, and these usages might be limited to very few cases. For example, when using "面目", we tend to focus on the impression we have after seeing one's face, like "面目清秀", "面目狰狞", besides, "面目" could also be used to imply one's hidden personality, the only usage I could think of is "露出了...的面目", which means some aspect of one's real personality becomes unveiled.

I think you must be confused by the meaning of "火车道上压过腿", because I think "压" doesn't mean "squash" here, instead it has a similar meaning with "stretch", which is derived from the phrase "压腿(leg press)". But I don't think "火车道上压过腿" has some concrete meaning here, it just helps with the rhyme. The whole sentence just means "I have been through a lot", in a more hilarious way.