This is one of the most difficult breeds for those who first decided to get themselves an indoor decorative dog. They are very, very dominant and if the owner does not control them, then they will control the owner.
Any owner will say that they are dominant in relation to other dogs. They will not bear it if another dog tries to take the highest step in the hierarchy and get involved in a fight. If several dogs live in the house, then the zwerg will always be an alpha.
Some are also aggressive towards other dogs and try to attack them. This is treated with socialization and training, but care must be taken when meeting other dogs.