CH₃CN (12–11) spectra of the K = 0, 1, 2, 3, and 4 transitions averaged over a beam toward the position of the dust continuum emission peak of the four sources embedded in the Main core of G31. The black lines indicate the different K components shifted to the frequency of the ambient gas velocity (96.5 km s⁻¹). The red arrows in the top left panel indicate the secondary absorption component at blueshifted velocities associated with source A.