Just looking now.. Mice have similar brain/body-mass ratio as humans. There is no strong (or visible) distinction in brain size between carnivores and herbivores in these comparisons:

https://en.wikipedia.org/wiki/Brain-to-body_mass_ratio#Compa...

You don't have to compare brain-mass/body-mass. You have to compare brain-mass/body-mass^(2/3).

> This phenomenon can be described by an equation of the form E = CS^r, where E and S are brain and body weights, r a constant that depends on animal family (but close to 2/3 in many vertebrates

I know this is the conventional wisdom but it doesn't really make sense. Controlling a sperm whale's body doesn't seem like a hard computational problem.

Echolocation in a "true" 3d environment is a very hard computational problem, which is why many aqueous mammals developed larger brains.

I assume you mean relative to controlling a human body?

Relative to anything smaller really.