  Shadows and spirals seem to be common features of transition discs. Among the
spiral-triggering mechanisms proposed, only one establishes a causal link
between shadows and spirals so far. In fact, provided the presence of shadows
in the disc, the combined effect of temperature gradient and differential disc
rotation, creates strong azimuthal pressure gradients. After several thousand
years, grand-design spirals develop in the gas phase. Previous works have only
considered static shadows caused by an inclined inner disc. However, in some
cases, the inner regions of circumbinary discs can break and precess. Thus, it
is more realistic to consider moving shadow patterns in the disc. In this
configuration, the intersection between the inner and the outer discs defines
the line of nodes at which the shadows are cast. Here, we consider moving
shadows and study the resulting circumbinary disc structure. We find that only
static and prograde shadows trigger spirals, in contrast to retrograde ones.
Interestingly, if a region of the disc corotates with the shadow, a planet-like
signature develops at the co-rotation position. The resulting spirals resemble
those caused by a planet embedded in the disc, with similar pitch angles.
