In the nightclub sequences, there seems to be more performers in their floor show than there are customers.
In the English subtitled version prepared for the 2009 U.S. DVD release, the subtitles give Kenji Sahara's character's name as "Asada" through most of the film. In the final fourth of the film, the subtitles properly give his name as "Masada."
The actress who plays the singer is singing in a much deeper voice than she speaks in (at least in the English dub)
Halfway through the movie, the H-Man is attacking one man on the ground while another man & woman watch. As the 1st man is almost dissolved, the 2nd man fires his gun 3 times based on the audio effects but there is visual smoke for just the first two shots.
When the men are exploring the abandoned boat, they are carrying lanterns, but the shadow of the lanterns appear on their faces an bodies. This is because the shot was lit from the camera's position, rather than from the actual lantern itself (which would light up their faces, not cast a shadow.)