A study by researcher Carolin Dittrich has revealed that some female frogs play dead to avoid mating, a behavior that is often associated with the Virginia opossum (Didelphis virginiana). She found that some European common frogs (Rana temporaria) she was studying exhibited this behavior during mating. The study was published in the journal Royal Society Open Science. Prior to this study, research had suggested that female frogs in explosive breeding species were passive during the mating process, but DittRich found the opposite. She observed three behaviors, including physically rotating away, mimicking a mating call and tonic immobility. Smaller frogs were more likely to go into tonic behavior than larger ones, which she theorized might be due to high stress.