Top: spectra of A and C, and their flux ratio, with emission lines at z = 2.383 marked. Regions with strong telluric absorption are shaded. The best-fit reddening from an SMC-like galaxy at the source redshift is overlaid on the flux ratio. Middle: bias- and sky-subtracted 2D spectrum from the night of 17 April 2021. Bottom: same 2D spectrum after removing the traces of A and C, revealing the trace of point source E. The C III] emission line is clearly visible, and the 1D spectrum can be found in Fig. 3. The spectrum of A shown in the top panel is from 16 April 2021, because the slit was unknowingly offset to the west, thus capturing more flux from A.