Maybe people don't know how to read hiragana and can't even tell what is supposed to be a scream? IMO, about the only hiragana I'd expect a good amount of the people here to know is "yu" for obvious reasons.
If there was more place in the word bubbles I'd give a more elaborate explanation, the diagram shows the yukkuri from the front, but Reimu hit the point on the back, and hence got the effect backward.