Toriyama Sekien
Concerning how there is a sluice depicted in the picture in the "Gazu Hyakki Yagyō" by Toriyama Sekien, the yōkai researcher Katsumi Tada and yōkai journalist Kenji Murakami posit that this is one kind of picture explanation by Sekien. According to them, the "aka" (red) can be understood as "aka" (淦, bilge water, the water that collects on the bottom of ships) and "aka" (垢, filth), so it is a metaphor for dirtiness, and the "shita" (tongue) can be understood as "shita" (下, down, in this case meaning the depths of one's mind), so it can be understood as the popular saying "the tongue (shita) is the gate to calamities", so the akashita is a type of rasetsu god, so the picture is likely saying that as long as one's mouth is open, one will never be blessed with good fortune.