For the scene where Dr. Stoner first injects David, Strother Martin actually makes a real hypodermic puncture on Dirk Benedict's arm with the needle.
All the venomous snakes featured were authentic and the cast actually did have to interact with them for filming. Only in the shot where Strother Martin grabs the king cobra's head during the show was a puppet snake used.
The poisonous snakes were not defanged during production. Five king cobras were imported from Thailand for this feature, ranging from 10 to 15 feet in length. They had been recently caught in the wild and were in good health with full venom capabilities. The "Snake Park" milking scenes were real and meant to mimic what Bill Haast did at his Serpentarium in Florida daily. About one ounce of venom was collected during each take, with no harm to the snakes. A different cobra was used for each take. The filming of this took most of a day, as the cobras spent most of their time trying to escape the fenced enclosure rather than raising up in the traditional cobra attack mode.
The mongoose in the movie was actually a tayra, a member of the weasel family native to tropical areas of Central America and South America.
The house used as Dr. Stoner's place was also used as the Garth Ranch house in The Virginian (1962).