Breasts can be shown in PG-13, although it can't be in a sexual manner.
Titanic is PG-13 and it has Kate Winslet full frontal!
Goddamnit, man! You done made me hurt my dick hand. (Phone Booth, 2002)

https://www.reddit.com/r/movies/comments/4zxuvb/which_pg13_movie_do_you_think_pushed_the_limit/

She looks like Pink.

There's about 3 or 4 instances of nudity in the Clash Of The Titans (1981) and that's a PG as well.

Lol i just noticed it this morning. Score.

Because they're just breasts and shown very briefly. There's movies from the 80's that are pg and show more then this movie.
I'm also oretty sure titanic is rated pg 13 and shows more then this movie.

I think it was because it was easily missed. I've seen this film quite a few times (first time when I was 18 when it first came out) and I never even noticed that until about 2 - 3 years ago.
Much like the difference of someone comically using the f-word in a passive sentence as opposed to screaming it out of hatred/anger. Quite a different context.

This message has been deleted.

You know what would be cool? A mass murder featuring bare breasted women during WWII.

Because at the time this film came out, it was believed that the brief glimpse of a woman's breast was less harmful to children than depictions of mass murder and extreme violence. Today we know better.

I am currently watching the film and I just noticed that! Came here to see if anyone knew about it!