I can take a lot of the story happening as it happens, but why exactly would Ulquiorra of all people decide it was a good idea to teach Twilight (and potentially the others) earth obscenities? Any one of us would probably jump at the chance, but why did he do it? And on that matter why would he ever bother with the types of obscenities that only Grimmjow and Nnoitra would freely use?
When spike sends him a letter asking why he would teach her the obscenities, and says she is driving him crazy with it, Ulquiorra's response to reading it is "Mission accomplished." She asked him to list words and phrases from his world. So it seems like what he wanted to do is see what she would do with this knowledge,and what would come out of it. So, ForScience? Possibly he only taught the ones Grimmjow and Nnoitra would use because those are the ones that come to mind fastest, probably hearing them over and over from those two.
Stop pickin' on the hospital staff, Thrush!
We're supposed to believe that Thrush has been bullying a significant number of hospital staff for a while. So how exactly did he wind up picking the one orderly that would have the nerve to turn against him, when going to Canterlot palace to basically kidnap Rainbow Dash and take her back to the hospital?
According to Word of God the only reason Corners spoke up is because Ulquiorra was able to trace the spell on Rainbow's wings to him with his pesquisa, which frightened him into talking. Another reason added would be the fact word of Ulquiorra's "specialties" are spreading and confessing all the things Thrush has done would at that point be the safest opportunity.
