Mode of Action
The mode of action we know about is an interruption of the Shikimate Pathway, a vital metabolic process in plants and bacteria (but not animals) that creates vital compounds such as folates and amino acids needed by the organism.
Glyphosate interferes with an enzyme used in that process, either by blocking the reactive surface of the enzyme or by binding micronutrients needed for its action. In either case, it is pretty obvious that glyphosate will prevent absorption of nutrients by the digestive tract, as well as starve beneficial bacteria that assist in digestion.
See also: