What to do with dangerously ignorant cats?

Nearly every time I cut something [e.g.food pack] cats run to me and, filled with curiousity, pull their noses right under knife blade. I try to cut things out of their sight and reach, but understanding my pets aren't afraid even of blades makes me worry. I won't be able to protect them always and anywhere. Is there a more or less safe way to teach them stay clear of sharp objects?