Lol, call me insane, but I have spent some time off and on over the years thinking about how a dog-pack for example would 'think' just using emotion and remembered events.
Initially words in my view are short cuts, wiped of much of their emotional context, which would speed up/enrich/diversify/ thought. Imagine if you had to parse that last sentence into emotional/memorized event language.

Beyond remembering seeing a chihuahua, and the last time they cut their paw, and maybe running... It gets real abstract real quick.
"Eating too much is bad for you" is easier though. That would translate.
"Bravery is an admirable quality" would also translate.
Thinking for yourself is one thing, communicating the product of that thought to others without physically demonstrating it in context is another. What spoken language did for us was to link up our isolated brains into one big uberbrain. Massively boosting our species. Writing set us free from death, at least knowledge-wise anyway.
I kinda think that any lifeform over a certain brain size, that runs/swims/flies in groups and demonstrates some kind of social order, is probably sentient. I mean still dumb as fuck compared to even the dumber among us, but still. We should feel bad about what we do to many animals just because they can't shout "Oi!!! please don't kill me."