The Sudden Object Test evaluates animals’ behavioural reactions to sudden and unexpected stimulus presented within their environments. It is designed to assess startle responses, approach–avoidance tendencies, and recovery following the sudden stimuli. This test is adaptable to various environments and all age classes. The test is designed for both individual and group testing. The test procedure described in this SOP is performed in a tie-stall environment, using either one of two object presentation methods on either a single animal or multiple animals simultaneously.