The original script was a Charlie Chan murder mystery titled "Charlie Chan at Trinidad" to star Warner Oland. However, due to Oland's untimely death, the entire script was re-written in only a few weeks to star Peter Lorre as his Mr. Moto character.
Last of Fox's eight Mr. Moto features starring Peter Lorre, but the seventh to be released (though completed two months earlier, Mr. Moto Takes a Vacation (1939) was distributed last). This was also the second Mr. Moto entry (after Mr. Moto's Gamble (1938)) that was originally written as a Charlie Chan script (and both entries were the only ones not directed by Norman Foster). The character returned only once, in a low-budget, black-and-white second feature produced in England, The Return of Mr. Moto (1965), starring Henry Silva.
According to Jon Tuska's "The Detective in Hollywood" Leon Ames claimed that Peter Lorre's teeth were in really bad shape, resulting in the star having very bad breath.
At 48 minutes, this is the same dock set as used in "Mr. Moto's Last Warning".
After Mr. Moto comes out of the swamp, his white pants are brown from the water. However, when he and Twister are locked up, his pants are dry and white.