Doodad turning around the x and y-axis?

The title's really vague, but I'll try to explain what I mean in this thread :)

I've seen in some terraining pictures doodads that are turned around their x and their y-axis. Normally, in the World Editor, you can turn a doodad around so that it faces a different angle.

I've seen in some terraining pictures, however, doodads that are vertically inverted and turned around (an Ashenvale Rock, for example, that's turned upside down or turned sideways). Is there a trick to doing this, or are they specially made models?

Thanks for the help,

- Omega-prime

No, they're not specially made models. You have to edit their pitch and roll values in the Object editor. Read them in here, the first post by Gitlich.

EDIT: Also here, concerning negative roll and pitch.