You saw a green figure with tears and blood stains on their smocks, they has their mouth exposed and has blood on their teeth, and injuries on their body, you recognized this green figure as a Zed, a infected grunt.

Zed: "RAHH, RAHH!" The Zed screamed at you and started running at you, you have a pocket knife in your pocket and hear other zeds nearby, you were in a alleyway alone with a zombie, What do you do?