Sabine Hossenfelder has made an interesting coverage of an effect that Vitor, Paolo and colleagues first discovered and explored: that of echoes from ultracompact objects without horizons. These objects are conjectured to arise in different scenarios, most of which inspired by quantum-gravity phenomenology. What they showed was that, if two of these objects merge, they give rise to gravitational-wave signals identical to those of black holes. What distinguishes the absence of horizons is that at very late times, repetitive echoes of the main burst appear. Hossenfelder's story is here.