Hmm... I needed to find a solution to fix it. I didn't want to throw the bottom pieces away as they do take some time to make. But because they are already fired, they turned into ceramics so a clay slib won't do to fix it. So, I just added some glaze to it and put new brain on it wit my clay gun. When the glaze will melt, the clay will stick into it like glue.
So hopefully I can add some zombie feelings to my shop soon! :)