Comparison of an optical-wavelength spectrum of SN 2018bsz with a model spectrum from Dessart (in preparation). C II line rest-frame wavelengths are indicated by black dotted vertical lines. In the case of the O II lines we draw vertical grey dashed lines that align with the peaks in the spectra and vertical grey dotted lines for the troughs (absorption). O I λ7774 is clearly observed in the model, but not in the observations, and is indicated by the vertical yellow dashed line. (The model spectrum is at around 40 days post explosion and around 10 days post maximum and therefore does not correspond to the same exact epoch of the observed spectrum of SN 2018bsz.)