Terror, Horror, Gross-Out, and Stephen King

Today is Stephen King's birthday. In his honor, let's play with a quotation of his.

"I recognize terror as the finest emotion and so I will try to terrorize the reader. But if I find that I cannot terrify, I will try to horrify, and if I find that I cannot horrify, I'll go for the gross-out. I'm not proud."

(I must say that it was hard not to leave the first word off of the quotation, after all what would be more appropriate than decapitating Stephen King. The worry would be that someday he might have cause to quote me and then would do the same because, you know, the traditional notion of justice dictates an I for an I.)

King distinguishes here between terror, horror, and grossing-out. What is the difference? Can you be terrified without being horrified? If you are sufficiently grossed-out, doesn't it bleed into being terrified by the image? Is this a meaningful distinction? If so, what's how do we account for the difference?