Forgive me if this question has been asked and answered already (though I don't think it has).
But while reading the Ishbal flashback part of the chapter, Scar's brother was talking about Xing alchemy. He said how negative/positive feeling will gather and will create a negative/positive flow.
So I started thinking (yes, I suppose this is more a theory then a question): Is it possible that, assuming alchemy is a thing of 'positive' flow, Father is able to create an area of 'negative flow', thus canelling out the alchemy?
That's all that was on my mind.
Sidenote 1: Winry's dad is cute
Sidenote 2: Riza's dad looks like he could be related to Shou Tucker :P