The reasons why zombies can't be smart or do math (lol) is because whats left of their brain is a rotting mess inside their skull. So the most they can do is grunt and push their bodies to the limit with their limited brain activity so they can give in to their sole purpose for existence... to feed.
There ya go! You learn something new everyday:)
The lip sync needs a lot of work.
You need some actual animation not sliding characters up against a background.
Overall, its a good start and keep animating:)