Ty so much man!!!
there are no checkpoints, the game allows you to save only after the day is over. It seems difficult but in reality it is not that difficult. Keep in mind that the demo refers to day 5, so with about ten missions behind you. I noticed that you entered the trenches to kill the humans, but you can easily shoot over the sandbags. Zombies must be hit in the head, there is no other way to kill them. I am modifying the knife attack because it was really difficult, now it is easier but I would keep it as a last resort. Thanks again for the video... see you soon a new demo. :)