This time, I happened to witness it.
First, the suspect checked to be sure the coast was clear.
Next, gnawing began around the lower portions of the bag.
Realizing some initial success, the suspect pulled vigorously on the bag until...
food flowed freely onto the floor, an unlimited supply of tasty Indoor Formula Morsels.
That is, until Mama got out the packing tape, now conveniently stored near the cat food.
Edited to add: The bag is now stored in the garage; the daily food is stored in a plastic container (Lily is busy gnawing on that, too). And yep, I could have stopped her from chewing the bag this time, but as usual, I wanted to document her naughtiness! :-)