No, you need the animals because they are unable to convince themselves that crystals have any effect.
They cannot know anything of crystals and their supposed properties, so if the animals in a group that are given crystals get better quicker, for example, than those in a control group who are not given crystals, this suggests crystals have an healing effect.
But if those who are given crystals get better at the same rate as those in the control group who get nothing, this suggests the crystals have no physical effect.
All animals - and humans, to a lesser degree - heal themselves, so there is no harm done to either group. We are just trying to find out if the crystals heal 'their' group better or more quickly.