What's up indeed. The first mention we get of this mysterious catcher in this mysterious rye is when Holden overhears a little kid singing, "If a body catch a body coming through the rye." Momentarily, it makes him feel not so depressed, in part because Holden is a fan of little children, and the only things better than little children are little children who are singing.
So that's all well and good until several chapters later when Holden's sister Phoebe corrects him; first of all, it's "if a body meet a body," and second of all, it's not a song; it's a poem by Robert Burns. Here's the poem itself:
"Coming thro' the Rye" (1796)
Coming thro' the rye, poor body,
Coming thro' the rye,
She draiglet a' her petticoatie
Coming thro' the rye.
O, Jenny's a' wat, poor body;
Jenny's seldom dry;
She draiglet a' her petticoatie
Coming thro' the rye.
Gin a body meet a body
Coming thro' the rye,
Gin a body kiss a body -
Need a body cry?
Gin a body meet a body
Coming thro' the glen,
Gin a body kiss a body -
Need the warld ken?
Now you're probably thinking the same thing we are, namely, what is all this about? Since you probably don't speak 18th century Scottish either, we'll translate for you. "Draiglet" = drags; "wat" = wet, "Gin" = when; and "ken" = know. In other words, Jenny is out in the rye with a wet body, dragging her petticoat – and she "meets" (has sex with?) someone. Need she cry (i.e., get emotional) about it? Need the world know about it? If not, then casual sex is OK. So that's what the poem's asking – is casual sex OK?
So…casual sex? Isn't that a huge deal in The Catcher in the Rye? Why yes it is. Holden's not so sure about sex in general, since he thinks that to get sexy with a girl is to degrade her, or treat her like an object. Therefore, he can't get sexy with someone he cares about. Casual sex is then his only option, but he's not so comfortable with that, either. The solution, it seems, is to avoid sex altogether, and to hang out with little kids and listen to them sing cute, innocent songs about…casual sex. Oops.
Even more ironic is that Holden says he wants to be the catcher in the rye – he wants to be "catching" all those little children. In his mind, this is protection, but clearly from the poem, the fun in the rye is more about sex than it is about preserving childhood innocence. This is rather sad, and possibly even tragic; Holden exists in a world that is steeped in sexuality. It's on the school walls, across from his window in the hotel, in kids' songs, and even in his seemingly innocent fantasies.