SADs were first interpreted as cross sections of magnetic flux tubes, which comprise coronal loops, that retract down due to magnetic tension after being formed at the reconnection site. This interpretation was later revised to suggest that SADs are instead wakes behind much smaller retracting loops (SADLs), rather than cross sections of the flux tubes themselves. Another possibility, also related to reconnection outflows, is that SADs arise from an instability, such as the Rayleigh-Taylor instability or a combination of the tearing mode and Kelvin-Helmholtz instabilities.