User blog comment:Yxz2014/Possible big plot hole??/@comment-25472766-20140930192150

I don't think it's a plothole.

Remember it was Hanje that theorized that eating a Titan shifter transfers powers. Ymir said she ate Reiner and Bertholdt's friend but were guessing she ate the whole body, which didn't happen to Eren.

When eren got his leg eaten by that Titan, he wasn't thinking about killing Titans at that point, he was stunned that their group lost so badly against the titans. When he got back up his only goal was to save Armin.

My theory is that if a Titan eats any body part of titan shifter will allow them to become a titan shifter. I think that a Titan Shifter can only have one ability so even if they eat other titan shifters, the power won't stack up. My guess is that the Titan that ate eren's leg became a titan shifter but the transformation back to human is slow and not instant. My other theory is that Reiner, Berthold and Annie have to kidnap Eren because if they take a body part from eren it will evaporate by the time they get back to their homeland. So they just take his whole body back to the homeland/village.