Juice is something like sensory feedback. In the case of this game it might be graphical hit effects, camera shakes and that sort of stuff. If the term juice is new to you, you might want to look into it. There are several GDC talks about this, such as this one:
Oh interesting. I was familiar with the concept, but I had never heard the term 'juice' used to describe it before. Thanks for teaching me something new!
