## Appendix A
### News  
We presented 20 news items to Fakenewslab users and asked them to decide whether the news items were true or false. However, as described in Section 3.1, the \"true or false\" framing is an oversimplification of a faceted problem. News flagged by fact checkers include click-baits, fabricated news, news with signs of cherry-picking, crucial omissions that frame a story into a new (malicious) narrative, and other subtle stretches of the truth. On the other hand, true news can also be borderline, open to a broader discussion. In order to offer a complex landscape of debatable information, we did not choose only plausible news from famously reliable sources, which would have been probably easier to spot in contrast with false news, but we also selected a few borderline news items, true news taken from blogs, and some with even a slight tendency to click-bait. The final sample thus included sometimes borderline and ambiguous pieces of information to process. In Table A1, we listed the 20 news items proposed in Fakenewslab, and in Table A2, we added some information on the source of the debunking. Every news item shown in Table A1 has been fact-checked in at least one outlet among debunking sites or mainstream newspaper from the following list: bufale.net, butac.it, ilpost.it, and open.online. According to tags adopted by fact-checkers, we classified news from 11 to 19 as false (see Table A2). News n. 20 is somehow an exception: we found it on an online website focused on health, openly against the 5G technology. Apparently, the news did not became viral, and it has been ignored by mainstream journalism and alsoby debunkers. The article suggests that the European Union has not assessed the health risks associated with 5G technology, which is clearly false (e.g., see the \"Health impact on 5G\" review supported by the European Parliament [[https://www.europarl.europa.eu/RegData/etudes/STUD/2021/690012/EPRS_STU](https://www.europarl.europa.eu/RegData/etudes/STUD/2021/690012/EPRS_STU)]([https://www.europarl.europa.eu/RegData/etudes/STUD/2021/690012/EPRS_STU](https://www.europarl.europa.eu/RegData/etudes/STUD/2021/690012/EPRS_STU))(2021)690012_EN.pdf accessed on 29 August 2022), and full of misunderstanding, to say the least, on how the European Commission funding processes really work. It should be noted that the most controversial classification, among the \"false\" news, is probably article n. 14. The source, \"La Voce del Patriota\", is a nationalist blog. The article refers to a factual event: a drugged Muslim man killed a elderly Jewish woman, and the reported homicide is mainly framed as racial, serving a broader narrative that criminalises immigration. When it was published, the trial was only in its first stage, and the acquittal was temporary, waiting for a rebuttal. However, a correction of the news was available at the time of our experiment in some debunking sites; in fact, further investigations dismissed the racial aggravating factors, stressing the drug-altered state of the murderer. This is an example of how difficult it could be to answer to a simple \"true or false\" game. The fact was true, but it was reported incorrectly. Nevertheless, we should recall here that our objective is not to judge people's ability to tell truth from falsehood but how a social media platform's