They can only eat what they are given, give them less.
Artemis, he is slithering on the grass becuase he dosent like the feel of the harness If you stick a piece of celotape (sp) to a cat if will rubb all over the ground (very funny )
I suppose they figure that it will rubb off if they rubb around on it, bless em
Keep trying and it will get used to it I suppose.
EDIT> Just read that teaspoon b0llocks lol, I tried taking mine for a walk a couple of times, I dont really see the point to be honest, they go really slow. Just feed them right and they will stay in shape.