Howanimals decide towithdraw from a contest has puzzled researchers for years. Currently, four modelstry to explain how this decision is made: war of attrition (WOA); cumulative assessment (CAM);opponent-only assessment (OOA); and sequential mutual assessment (SAM). Although their predictionsdiffer, they must be simultaneously tested to infer which model best describes contests. Herein, weidentified the traits related to the resource-holding potential (RHP) in the decapod Aegla longirostri, andused these traits to test the predictions of each model. We identified which morphological/performancetraits affect contest outcome, related these traits to the contest duration of male dyads, and tested thedifferences in aggressive acts (claw grabs). We tested the models using pairs of random and RHP-matched opponents. Additionally, we performed contests where RHP-matched opponents couldcommunicate before the contest (‘previewed’), and contests where the focal animal would onlycommunicate with one individual and fight another unseen individual afterwards (‘unseen’). Incomparing these groups we tested whether information was being exchanged. The best predictor ofcontest outcome included a combination of cephalothorax length and claw height, and claw grabsincreased with opponent similarity. Contest duration increased with loser's cephalothorax length anddecreased with winner's cephalothorax length in random pairs, and winners spent more time in clawgrab than losers. These findings refute WOA and OOA. In RHP-matched pairs, no relation was found andcontests with previewed opponents were shorter than contests with unseen opponents, both resultssuggest SAM. However, the time spent in claw grab did not differ between previewed and unseen op-ponents. We argue that SAM is cognitively complex, and mutual assessment without comparison of RHPcould be a better explanation. Furthermore, claw grab is important in contest resolution. Thus, the costsinflicted may suggest a mixed assessment strategy for A. longirostri's contests.© 2014 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.