What does it mean in "Friends" when...?

Question

It's in "The One When Ross And Rachel...You Know" and they're up in the planetarium, and Rachel roles over onto this juice carton and it squelches and this happens:

RACHEL: Ah, oh God. Oh, honey, oh that's OK.

ROSS: What. Oh no, you just rolled over the juice box.

RACHEL: Oh, thank God.

What is it that she's worried that happened. Sorry I know it's a strange question but it's been bugging me, I know that it's probably something really obvious! Thanks!

Answer 1

She thought Ross was so excited that he may have "peaked too soon" (prematurely if you like).  If you are 18 or over you should understand, if you're not, then you probably shouldn't know...