Before revision:  We discuss different models that can capture potentially destabilising self-referential feedback loops, induced either by herding, i.e. reference to the peers, or trending, i.e. reference to the past, and account for some of the phenomenology missing in the standard models.
After revision:  We discuss different models that can capture potentially destabilising self-referential feedback loops, induced either by herding, i.e. reference to peers, or trending, i.e. reference to the past, and account for some of the phenomenology missing in the standard models.