A no-tech card game designed to give learners an insight into how assessors and examiners use Turnitin's originality checking service to identify potential plagiarism.The game uses two decks of cards. The first simulates the decision making process, presenting a series of extracts from Turnitin reports and asking students to judge whether they show examples of plagiarism or not. These are then compared to a model answer (which is open to debate - many of the examples are borderline) and students asked to reflect on and challenge any disagreement.The second deck of cards is introduced, these show descriptions which match up to the first deck, and provide a competitive element as groups compete to solve a word puzzle by correctly matching the pairs of cards. This emphasises how nuanced the inferences that can be drawn from the report are.Uses of the resourceSimilaritySim can be used in several ways.Teaching how to understand Turnitin reportsWhere learners are given access to reports on their own work, this activity can be used as part of a session introducing them to how the reports are interpreted, and how to avoid common mistakes (eg paying too much attention to the % score).It can also be valuable in staff development sessions, to train staff who will be interpreting the reports in a scaffolded way that can be more engaging than simply showing examples on a screen.Academic integrity trainingSimilaritySim can be used to show students the range of types of unoriginal work which Turnitin can detect, which can help them to understand the difference between switching out a couple of words and proper paraphrasing. (Although care should be taken the importance of not plagiarising, rather than merely beating Turnitin).Reducing anxietySome learners are quite nervous about submitting high stakes work to Turnitin, mainly due to misunderstanding the way in which Turnitin is used. This activity shows them that their assessor will need to spend considerable time working with the report, rather than it being a "computer says no" scenario.