He might have been hoping for a slightly less technical (or more plain English) answer. A quick reading of that reference sounds like it works by increasing the permeability of the cell membrane to chloride and hydroxide ions to disrupt cell function (since the cell can't regulate those ions properly in the presence of trichlorocarbanilide).
If someone would like an explanation more intermediate between the very simplified one I provided and the very technical one in the article Ouabache linked to, ask away!