A very thin line. And a dot.

Call Julie.

An ordinary command--a statement instead of a request, as indicated by a period at the end, rather than a question mark--becomes elevated in importance with the simple, continuous application of the shift key:

CALL JULIE.

But with a line hovering over that period, the urgent all-caps statement seems not only more urgent, but friendlier too:

CALL JULIE!

as if what it's really telling us, in sideways Morse-code-like style, is that the inflection of the last syllable is not a commanding drop but a cheerful raise in pitch, followed by an innocent but knowing smile, and that behind that narrow facade is a big fat "This is of the utmost importance, but I know that implied cheeriness is more likely than actual bossiness to get you to actually do it right now (please)." It may also say "Whoops, I almost forgot to tell you this, and I cannot possibly hold back any longer for if I do, I shall either forget again or explode."

So, as you can see, there is a very thin line dividing [an ordinary statement.] from [an EXCLAMATION!].