A comparison of the ¹²CO P(6) and ¹³CO R(6) line profiles from GSS 30. The two profiles should be similar, including absorption from the same lower level. The absorption in the ¹³CO line is deeper and redder than that seen in the ¹²CO line, despite that the ¹³CO line cannot be more optically-thick than the ¹²CO line. Instead, we infer the presence of redshifted absorption from infalling gas at 10−20 km s^-1. The broader emission is produced far enough from the central source that it does not travel through the infalling gas and consequently does not suffer from absorption.