We've noticed over recent weeks/months, that Billy's large sack of (very expensive) dry food has been 'interfered with'.
We keep his food in the studio. It's in a 10 kg bag, which we've occasionally found knocked over, clawed at, and generally mauled. It's been obvious that some creature has been helping itself.
This morning I found it dragged about a foot away from where I'd left it, claw marks all over it, and a good handful of 'croquettes' over the floor. I eliminated all previous possible culprits, and turned my attention to the cat flap, and one renowned local wild cat.
I've now locked the cat flap, and also secured it from both inside and outside with metal grills and a heavy flower pot. If the devil can get past all that, then good luck to him.