Its Contagious
cows_make_milk
Its Contagious
I'm opting towards human because when you first meet susan you see that they all have gills and what not.
But when you see her a second time to request their help he seems surprised when she lets him feel her neck. If she was a kinda fish person he'd have been disappointed instead of just surprised and dazed as the two left.
Well that's what we are implying but we don't know for sure. Maybe he was too shocked to have found out that he didn't know what to do.
Did you clearly see his face at the end, he was purely surprised and had a look of awe struck rather then one of disappointment since finn wanted to know that there's at least other humans then just him.
I did, I watched it recently. I still believe there is mystery behind it. It can be interpreted both ways.