An oath on a deposit - to make it clear that it's not in the person's possession, for example. A deliberate false oath of deposit means a korban asham - a guilt-offering. Back when they were studying Shevuot in yeshiva in the time of the Gemara - witnesses warn the person not to swear falsely. Note - the korban asham is fairly unusual, in that it is itself the punishment, or the guilt, and not for the sake of atoning. Plus, Rav Kahana's question about witnesses warning against false testimony - but is that warning a halakhic warning for all sins, in general? It would seem not. Also, a refinement - the guilt-offering only is incumbent when the false oath is intentional - and without witnesses. Plus, the way the oath for the deposit has more stringent halakhot than those for the oath of testimony.