I wonder if Titans are humans that caught some virus?

I tolerate the armoured titan wall breach, only because the scene was rather nice. But realistically, breaching that wall as going through butter without a scratch and without much of a slowdown is a bit too much. I'd understand if he broke the door and then go slowly from there with the help of others...

Now regarding the walls, I'm wondering if Titans can swim. Why? because that could be an explanation for the boats, but maybe not with the way they move and how giants could handpick people easily...

Now that we've had those 2 eps, I wonder what will fuel what's to come.