Why did my professor get so hostile?

I had my professor inspect my design work on my laptop to get it approved; an example was to get ideas/suggestions from her. My apple laptop was on a table a few feet away from her desk, and we were looking at my screen together while sporadically communicating. During that, someone suddenly went up to her because he needed her then both of them walked away and talked. After he finally left the room, I waited for that professor to resume looking at my work on my laptop. Since I waited for a really long time, I assumed she just forgot. So, I finally lifted up my laptop and carried it over to her when she happened to be standing less than a foot away from her desk. When she saw me, I expected her to be like *Oh* Instead, she suddenly snapped really loud with clenched teeth & wild eyes, "You need to print those out, Kathy!"