Obviously directly inspired by The Thirteenth Chair (1929) starring Bela Lugosi, with the group sitting in a circle in a seance of sorts (here, a trance) and the murder occurring while it's in progress. A knife is the murder weapon in both cases.
The two voices Jessica uses while hypnotized are imitations of Bette Davis and Mae West.
José Ferrer played a hypnotist for the second time in his career in Death Casts a Spell (1984). The first time he portrayed a hypnotist was in Whirlpool (1950).