science

I think the ability to amass, retain, and augment information learned by our ancestors is our killer feature. Storytelling is an important part of it, using rhythm and rhyme to help us remember and pass on those stories, being able to encode those stories as art and writing, they're all ways to make it easier for the next generation to get up to speed quickly and then push the boundaries of understanding even further, instead of every generation having to relearn all the basics the hard way. It's not perfect and it's still incredibly lossy, but I think that's why we broke out and became, I think it's fair to say, the dominant lifeform on the planet. Is that the bar for sentience? I don't think so, but I don't really have a better one.

Also we invented santa claus to teach kids that every authority figure in your life will willingly engage in a conspiracy to gaslight and bribe you in order to make you behave the way they want you to.