Comparison of spectra from selected dense gas tracers (black) with scaled-down versions of the CO(2 − 1) spectrum (red) to illustrate the existence of two different chemical components in the wing regime of the L1448 and I04166 outflows. Note how in the SO, CS, and SiO spectra, the fast wing (f-wing) component matches well the CO spectrum, while the slow wing (s-wing) component follows a different trend: in SO, it matches the CO spectrum, while in CS and SiO, it lies below it. In contrast, the H₂CO wing matches the CO s-wing but lies below the f-wing at higher velocities. This different behavior of the spectra in the s-wing and f-wing regimes suggests that the composition of these two parts of the outflow follow different trends and need to be studied separately.