blushing

Yesterday in class, I did something quite embarrassing. After most of the laughter quieted, one of my students said I should "slice" about it, and since it still is making me blush to think of it, I guess I will.
I currently teach pre-service teachers in a private religious university. Yesterday, in our discussion about grading, I intended to say grade sheets, but I accidentally slipped my vowel from a long "e" to a short "i." First, incredulity--on my part and my students' faces. Then they laughed. And me? Red face. Hot face. Cover your face. Why is that an instinct? Do we, like my grandson, think that if we close our eyes no one can see us?
The problem after that was that every time I attempted to say the word sheet, the other word felt like it was going to slip out! I changed to rubric and paper. This probably isn't a big deal to some people. But that isn't a word I say--and even if it were, it wouldn't be one I would say in this setting. So, like most embarrassing moments, it flashes back into my mind and then my face responds, blushing all over again. Even here, in my office, where no one is watching.