This bag appears as a typical sack — possibly appearing to be empty, possibly as having beans in its bottom. 

The sack is, however, the lure used by an extra-dimensional creature. It is one of its feeding orifices. Any substance of animal or vegetable nature is subject to "swallowing" if it is thrust within the bag. 

The bag of devouring is 90% likely to ignore any initial intrusions, but anytime it senses living human flesh within, it is 60% likely to close and attempt to draw the whole victim within — base 75% chance for success less strength bonus for "damage" each + 1 = -5% on base chance.

Thus an 18 Strength character (with +2 damage) is only 65% likely to be drawn into the bag, while a 5 Strength character (with -1 damage) is 80% likely to be drawn in.

The bag radiates magic. It can hold up to 30 cubic feet of matter. It will act as a bag of holding (normal capacity), but each turn it has a 5% cumulative chance of "swallowing" the contents and then "spitting the stuff out" in some non-space. 

Creatures drawn within are consumed in 7 segments of a round, eaten, and forever gone.