The placement of a fully formed foot inside this child's brain shows how developmental programs are hard-wired in our genome. Once a cascade of transcription factors is triggered in a group of cells, it can autonomously create a full body structure such as a leg. In this case, something inappropriately triggered the cascade in the wrong place. Hopefully someday, we'll understand what causes things like this. Then, we might actually be able to re-grow structures for other unfortunate people who need an organ replaced.
I hope this kid is okay.