how does montmorency irritate the friends as they pack? what makes him do such things

From the text:

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.