Sinusoidal-type patterns in single-spaxel spectra extracted from the drizzle data cube with a spaxel size of 0.05″. Top panel: LBQS 0302−0019 spectrum integrated over an aperture of r = 0.5″ (orange curve), in comparison with the spectrum of the brightest spaxel (blue curve). Both spectra are normalised to their maximum values, for visualisation purposes. The wiggles affecting the single-spaxel spectrum are reported in grey and are obtained as the difference between the blue and orange curves (after subtracting a low-order polynomial function that takes the differences in the continuum level into account). Bottom panel: wiggles obtained from the eight pixels closest to the brightest one. These wiggles strongly affect the shape of the continuum and, in particular, the Hβ profile and the wings of the [O III] lines. See Fig. B.1 for analogous effects in the emsm cube.