Looks fun. Congrats on learning React. I haven't wrapped my head around it yet. (But then again, I avoid front-end like the plague...)

I found an "undefined" thing: http://d.pr/i/Dd2eA

Also, the steps aren't really clear. I got "tener - to have" and "Yo", and I put in "tengo" and hit Enter, and it took me back to the main page, where I had to hit "Play" again. I would have expected it to give me another tense or another verb, but that's not what happened.

I tried again by hitting the envelope arrow, but it basically did the same thing.

It's a neat concept (and reminded me that I need to retake Spanish 101) but it could probably use some more documentation and testing. Hope that was helpful!