It's self-awareness, at least in general and as considered by a court when granting it to a chimp.
It's also why I would likely never go vegan, although I do advocate for a drastic overhaul of animal welfare standards.
* or 5, if this list also has "personhood" in it
No, not really. It has pretty standard definitions in philosophy and science, or it wouldn't have been able to be tested for over several decades. I suggest spending some time reading the wiki, it gives a pretty detailed overview.
The only point you have is about consciousness, and we don't need to understand the entire thing to understand parts of it or observe it, just like gravity.
Besides, if you believe animals are not self-aware, why d you care about "welfare"?
Most medical professionals and ethicists consider 24 weeks to be the reasonable cutoff for abortion because this is when the fetus starts to develops sentience.
The reason this is relevant is because that is the first stage of development capable of having an identity relationship with the future person that fetus/infant will become.
Animals don't have to be self-ware to suffer. Not introspectively self-aware at least.