Sweet Caroline by Neil Diamond is featured in Mash-Up, the eighth episode of Season One. It is sung by Puck while playing his guitar as a "personal tribute to a musical Jewish icon," Neil Diamond.
This is his first solo performance on Glee. He sings it for the group after Rachel says to Puck that she needs a man who is brave enough to sing a solo for her. In order to stay in a relationship with Rachel and prove to her that he can do it, Puck sings this song in front of the whole Glee Club to Rachel. However, Quinn seems very impressed by the solo and stares at Puck longingly. The rest of New Directions join in towards the end.
Puck:
Where it began, I can't begin to know when
But then I know it's growing strong
Was in the spring
And spring became summer
Who'd believe you'd come along
Hands, touching hands, reaching out
Touching me, touching you
Puck with New Directions
Oh, sweet Caroline
Good times never seem so good
I've been inclined to believe it never would
Oh, sweet Caroline
Good times never seem so good
I've been inclined to believe it never would oooh oh no..
Trivia
This is Puck's first released solo.
Puck sings the song for Rachel to show that he can sing a solo and that he can handle her. This is the first song that is dedicated to Rachel.
A longer version of this song was later released where you can clearly hear the New Directions doing backup. Source
Errors
As Puck is singing Sweet Caroline to Rachel, they show Brittany sitting in front of Quinn. When the camera zooms in on Quinn, the chair in front of her is empty but as the performance ends, Brittany is shown in her seat again.