It turns out that most of the items on Mann's list qualify as food, though they may not show up on the menu at Le Bec Fin. Cat food isn't the healthiest choice for humans, for example, because it contains too much fat. Chicken bones can be ground up, or even munched on whole. Even urine could be considered food in the direst of circumstances. A lot of people have survived by drinking urine.
Ants also survive the cut, being a fine protein source.
It's really quite good. Grass gets disqualified, because humans can't digest the cellulose in it, and it will make them sick. Rats, city pigeons, and tabby cats, on the other hand, are wholesome enough. One student struggles to verbalize her aversion. It's the whole psychological aspect.