This sentence would probably be a citation in APA style. Citations on research papers are very important since they give due credit to the original owner of the statement. Statements that don't have citations tells the readers that those statements are of the researcher/s alone which would be a problem for them if found out that it wasn't theirs to begin with. This would result to a work of plagiarism which is a grave sin in constructing research papers and is more equated with the act of stealing.
a lightning stuck in-between them and the world split in half seperating them from eachother
explanation link: every4explaination.com
Yes, one should make sure that the subjects and verbs agree
