The reasons are two here – first of all, theweights are easily controlled, since they are small and they arehard. The dog, on the other hand, is softer, and if he gets relaxed,he will tend to slip all over the place, making it harder to holdhim. Also, I assume that you did not do curls with him on your hands,but rather held him still, and this is a completely different kind ofload – it is a static one, and it puts to test your endurance, notyour strength – these are two different concepts.