Unexpected/unpredictable sensory shocks, (for example a large sudden movement or sound) can cause significant issues for people with some cognitive impairments, particularly autistic spectrum. In some cases the level of distress can be intense, enough to force them to stop playing immediately and take some time to recover.

Although unexpected actions are a typical element in many game mechanics, if the mechanic does not require them (for example turn based strategy) or designing specifically for an audience with a high prevalence of cognitive impairment, they should be avoided wherever possible.

Best practice example: Civilization V