It's a normal size, looks like any other chicken. Except it has evil eyes and a cackle. Not only a slow one, it seems to be able to display a range of different cackles for every occasion.

Kahlan carefully moved her trembling hand away. The chicken-thing cackled softly with satisfaction.
Lightning flashed again. She didn't need the light, though. It was only inches away. Close enough to feel its breath.

Et cetera, et cetera.
It's sometimes hard to believe I suffered through this kind of thing for the awesome characters.