A total of 50 adult male CD-1 mice at the age of about twelve weeks were used in the study. All mice were laboratory-born and thus predator-naïve.

The mice were exposed to seven different odourants. Six of them are sulphur-containing compounds found in the body odour or secretions of natural predators of the mouse and one is found in fruits. All odourants were presented at a concentration which is a factor of 100 above the olfactory detection threshold of mice.Three of the odours were additionally presented at concentrations which are  a factor of 10 and 1000 above the detection threshold. The odourants were diluted with the near-odourless solvent diethyl phthalate. The solvent was also used as the “BLANK” stimulus in every test.

Each mouse was individually put into the testing arena, a modified standard mouse cage (40 x 25 x 15 cm), subdivided into two equally sized compartments by a vertical plexiglass wall attached to the lid, with a semi-circular opening at the bottom which allows a mouse to switch between the compartments. The two-compartment chamber had a perforated floor, and under the floor of each compartment it had a petri dish with a filter paper impregnated with either 100 µL of odourant or 100 µL blank stimulus.

The time spent in each compartment was recorded continuously for ten minutes as an indicator of aversion or preference for one of the odours. The number of switches between the compartments was recorded, as an indicator of the overall activity level of the mouse. Additionally, the number of faecal pellets dropped during the test per compartment was recorded, as an indicator of the animal’s anxiety level.