Ha ha, it may be completely irrational but I'm totally in that set of people that have trouble with this. Maybe it's just my love for the dragons, but there are generally rules about what these zombies can and can't do and even if the King foresaw what was coming and found chains to get the dragon, they shouldn't be capable of swimming to the bottom to find him and wrap them around him to drag him up. Right? GoT writers can't just willy nilly change the rules on us! It's not fair!!!! lol