Well in the first episode , the incident was as follows:
Phoebe catches cold and because of that her voice becomes little harsh but she thinks that adds a peculiarity to her Singing. But soon she gets well but Monica catches it, so she does all the weird stuffs to get it back so that she can again sing like when she had cold. But unfortunately despite all her weird efforts she fails to catch cold. Then at the coffee house, just when Gunther was serving coffee , he sneezes. Seeing this Phoebe asks him to kiss so that she can catch the cold and before Gunther could react, she kisses him.
Now the funny part starts , at the end of the episode when they are running the credits, Gunther approaches Rachel and following is the conversation that goes.
Gunther: I don't know if you heard about what happened between me and Phoebe the other day_
Gunther: Well, we kissed. I-I-I didn't initiate the kiss, but-but I also didn't stop it, and I've been feeling guilty.
Rachel: (confused) Okay.
Gunther: So umm, are we cool?
Rachel: (really confused) Okay.
Gunther: I knew you'd understand.
(Gunther walks away, leaving Rachel with a `What just happened?' look on her face.)
Well in the following episode another incident happens between the two, which goes like this...
[Scene: Central Perk. Rachel is sitting on the couch alone working on a crossword puzzle. Gunther is there, going into the back room.]
Rachel: I did it! Oh! I finished it! I did it all by myself! And there's nobody to hug!
[From the background we hear a crash and Gunther comes running out of the back room, pushing people aside, reaching for Rachel.]
[Gunther slips and falls just before reaching the back of the couch. Monica and Phoebe come into Central Perk.]
Rachel: Hey! Hey, you guys, I finished the crossword all by myself! Hug me!
[Gunther gets up slowly from behind the couch and walks away sadly]
Poor Gunther...........Still remember him expressing his love to Rachel in the last episode of last season and she like most, not taking it the way he meant, just replies I love you too.....