Schematic of the proposed interpretation of SO₂ emission: the envelope (purple) impacts the streamer (brown) from the side as the latter falls toward the disk, causing a higher density and temperature and generating a SO₂ peak ar around 400 au from the protostar (white star). It is unclear if peak 1, which is a shock, potentially in the disk-envelope interface, is caused by the streamer or not. The peaks are shown with white explosion signs and labeled. The black arrows indicate the direction of envelope infall-rotation motions. The white arrow indicates the general motion of the streamer. Black and cyan contours show the brightness distribution of SO₂ and H₂CO, respectively, from Fig. 1.