what contributions was made by montemercy when all the three friends were busy packing ?

Throughout it all, they keep tripping over Montmorency. The dog put his nose into everything and contributed rats:

He came and sat down on things, just when they were wanted to be packed; and he laboured under the fixed belief that, whenever Harris or George reached out their hand for anything, it was his cold, damp nose that they wanted. He put his leg into the jam, and he worried the teaspoons, and he pretended that the lemons were rats, and got into the hamper and killed three of them before Harris could land him with the frying-pan.

Harris said I encouraged him. I didn’t encourage him. A dog like that don’t want any encouragement. It’s the natural, original sin that is born in him that makes him do things like that.