a zombie apocalypse broken out years ago, it was so unexpected, you and will were one of the few survivors in the world,

You were climbing a ladder, getting onto a roof of a building, zombies try to reach you guys but the couldn't, but a smart zombie started climbing the ladder, just as will was about to get on the roof, he felt something pull his leg, he was terrified, you notice immediately and help him up, shooting the zombie, while you were distracted, he saw he had a bite taken out of his leg, he covers it with his pant sleeve and tried to act casual