Schmoo always had a soft spot for cat food. It's just so meaty and delicious and those jerk cats get it so why not him?
We were never around to witness these capers (this happened a couple times), but as best we can figure Chewy initiated the plan and Schmoo seized the opportunity to capitalize on it when he saw his opening - his forcefulness banishing her to some dark corner to skulk...and wait.
On these occasions his midsection really would balloon up to twice its normal size. We never really had the heart to scold the little guy. His subsequent discomfort was enough punishment, I suppose. Schmoo was an opportunist and waving our arms around, raising our voices at him wasn't going to stop him from doing it again. He knew what he'd done was wrong - he'd known while he was doing it - but that wasn't going to stop him from doing it again once we let our guards down. This approach might seem a touch indifferent, but Schmoo was gonna be Schmoo. His physical limitations afforded him few opportunities for any real mischief, so why begrudge him these small victories over routine?
In the end, all we could do is laugh and shake our heads in embarrassment when forced to take him out into public while we waited for him to shrink back to his normal size. With the ensuing diarrhea, that typically took about three days.