From the Wiki page for Furin

> ...must be cleaved by furin or furin-like proteases to become fully functional. Anthrax toxin, pseudomonas exotoxin, and papillomaviruses must be processed by furin during their initial entry into host cells.

From the sound of this:

- the site on the virus gets cleaved - Furin enables the cleaving - Furin exists in hosts cells

What I think I understand is, the cleaving makes it easier for the virus to reproduce inside the cell?

edit: turns out I have no idea how to format things on HN