How easy it can be to incur unintentional duplication. A case of "self-plagiarism"

Using the definitions of the International Committee of Medical Journal Editors1 “a duplicate publication is the publication of a manuscript that substantially overlaps with one already published without clear, visible reference to the previous publication”. We wrote this letter to make public and transparent a case of unintentional duplicate publication, described below: Looking for a suitable journal in which to publish the article entitled “The pH of guinea pig (Cavia porcellus) meat from the welfare-deficient slaughtering in the Peruvian central Andes”, it was identified potential veterinary journals or scope-similar journals (e.g., agricultural sciences), to expand our universe of eligible journals for this type of studies. Two proposals were selected, and although the journal "FAVE-Ciencias Agrarias" (ISSN: 2346-9129) was initially considered as the first option, since it was indexed in Scopus, it was finally decided to publish in the "Revista Veterinaria" (ISSN: 1669-6840), also indexed but more related to the proposed topic. Therefore, the format of the article originally entitled “The pH of meat of guinea pig (Cavia porcellus) for human consumption in the Peruvian central Andes” was submitted following the guidelines of the "Revista Veterinaria". Before making this decision, the cover letters were prepared for each journal in which the publication copyrights were transferred to each of them. Both documents were enclosed in an e-mail that was also provisionally addressed to the e-mail accounts of the two editors of the journals and awaiting an internal agreement between the authors to decide to which of the two e-mail addresses and which of the two cover letters would remain when sending the final version of the article. From the authors' perspective, a crucial moment, for being the origin of this unintentional and negligent error, was on May 10, 2017, when we submitted the article via e-mail to the editor of the "Revista Veterinaria" but with the cover letter and, consequently, the copyright transferred to the journal “FAVE-Ciencias Agrarias”. Even worse, all these documents were inadvertently and mistakenly sent to the e-mail addresses of both journal editors. With an automatic reply mail from the "Revista Veterinaria", we were informed of the reception of the article. Weeks later, on June 23, we were contacted by the Journal "FAVE-Ciencias Veterinarias" (ISSN: 2362-5589); we had not had any contact with this journal, nor had we considered it unt