When you are rescuing the prisoners in Chapter 5 and have a challenge, there is usually a Finish Challenge can in the room.

Go to the infirmary and you will find a medusa. Kick the thing with bottles on top. You find a freeze can. Get it, then throw the bottles at the medusa to kill her. Then talk to the bearded person and zombies will appear. Go to the place where there are two ghost cans. Take only one of them. Go inside and there will be a tipped over locker. Kick it to complete the challenge.