 Perhaps the most fascinating feature of quasi-local black holes is the fact that, in a sense that can be made precise, they are “clairvoyant”: they are aware of and respond to changes in the geometry in spacetime regions that they cannot be in causal contact with (Bengtsson and Senovilla 2011). Indeed, they can encompass regions whose entire causal past is flat! This subject exemplifies the exuberant weirdness that causal structure in general relativity can manifest. 