Under the Barbarian Lesser Hurling rage power we have:
PF SRD wrote:
Benefit: As a full-round action while raging, the barbarian can lift and hurl an object up to one size category smaller than herself with both hands or two size categories smaller with one hand as an improvised weapon with a range increment of 10 feet. This inflicts damage as a falling object plus the barbarian’s Strength bonus.
So if a medium sized barbarian wanted to pick up and throw a rock one-handed, this would mean that the rock would have a tiny size category.
If you zip on over to the falling object rules however the table doesn't give the whole spread of size categories, only going down to size small that causes 2d6 damage.
This becomes more of a problem if you have a small sized barbarian who has this rage power and wants to throw a one-handed rock, as now the size category of the rock shifts down to diminutive.
So at the very least it would be helpful to clarify the fall-object damage chart. Since a small sized barbarian could have reduce person put on them, it might as well get the damage all the way down to fine size.
