[FaceKicker]

Both your URLs go to the same page (was going to say they were the same URL, but they're not). Maybe [1] was supposed to be the below?

[1] http://www.ncbi.nlm.nih.gov/pubmed/25430774

[carbocation]

You are correct; they both go to the same page. One is a direct link to Doudna's comment, the other to Charpentier's comment on the same page... but since the page is so short, there is nothing to scroll to, so they look like they are the same link.