Use your sense of justice, when you judge nonhuman animals, use your common sense, when you judge animals.
When natural scientist make findings about how an animal brain works, how animal psychology works, cognition, consciousness, it means they will do 1. invasive research at some point, and 2. they will be using parameters that are strictly homoncentric, meaning the frame of reference they apply moves only within a “human” framework of “objectivity”.
A real Animal Rights revolution would require people to step back from human parameters. A real Animal Rights revolution would mean we as humans are able to face nonhuman animals on the level where we allow them to be different but still respect their untouchable integrity in this natural world that we all live in and are born into.
When we want to give nonhuman animals our definitions, we should as Animal Rights people make sure we don’t impose a worldview onto them and their concerns, that is not theirs (and thus not in THEIR interest). If we can’t accept that animals have their own views of the world, then we deny them real and autonomous subjectivity, and then we deny them personhood in a sense that we should respect.
We don’t need scientific proof and scientific arguments, what we need is to learn to accept common sense as a basis for morality and moral judgment in Animal Rights issues as much as we accept our basic common sense to be enough when we talk about each other or internal human concerns.