You can search the MPA movie ratings database to find the reasons movies got their ratings:

Blind Swordsman: Zatoichi, Rated R for strong stylized bloody violence.

Reign Of Fire, Rated PG-13 for intense action violence.

Pitch Black, Rated R for sci-fi violence and gore, and for language.

Princess Mononoke, Rated PG-13 for images of violence and gore.

Kill Bill Volume 1, Rated R for strong bloody violence, language and some sexual content.

Ghost In The Shell II: Innocence, Rated PG-13 for violence, disturbing images and brief language.

Ghost In The Machine, Rated R for high-tech horror violence.

Evil Dead, Rated NC-17 for substantial graphic horror violence and gore.

Lord Of The Rings: The Two Towers Rated, PG-13 for epic battle sequences and scary images.

I just find the descriptions amusing for some reason. Sometimes you have “violence” and other times you have “substantial graphic horror violence” or “intense action violence.” I’m curious how they found gore in Princesss Mononoke. I remember some blood, but nothing I would consider as “gore.”