About the Trident joke, it's a reference to ad about the chewing gum, Trident. The brand had an ad that said "4 out of 5 dentists recommend chewing their sugarless gum" or something along those lines. So when Rachel walked in the room very excited to share some news, Chandler was his usual sarcastic self and asked if the 5th dentist (the 1 out of the 5 dentists in the ad who did not recommend the Trident sugarless gum) finally caved in / gave in to the recommendation of chewing Trident gums. On no.3, so the gang are at the wedding rehearsal for Phoebe and Mike. Chandler and Monica comes in and Chandler throws a sarcastic remark "I so rarely get to practice my meals before I eat them". Wedding rehearsal dinners aren't a thing in my culture, but I reckon it's a bit of practice for what happens the next day (actual wedding day), as well as a dinner with the bride's and groom's practice. So, in Chandler's joke, the wedding rehearsal dinner was = practice for the actual wedding day dinner. And practicing for dinner / to eat sounds a bit ridiculous if you think about it, so he was sarcastically saying "Oh yey, we're practicing to eat (tonight at the wedding rehearsal dinner) before we actually eat (tomorrow at the wedding). That's good because we rarely do that." Insert sarcastic face. And then Phoebe, to remind Chandler that he previously promised her and Mike "no stupid jokes" as a wedding gift to them, asked "Okay, what did you say was your one gift to us?" to get him to stop with this sarcasm and jokes. Hope that helps.