Poisoning the daiquiri
Where did she get the poison and have a chance to administer it?
Plus she's able to poison her own coffee in full sight of the production crew and conveniently not be seen!
From her collection of prescription drugs.
Codamol (sp?) is an American brand, which is what Elizabeth Taylor's character takes. Remember the secretary's comment about 'trucking a gallon in' when asked about Codamol?
On its own Codamol is relatively harmless, but dangerous when mixed with alcohol.
Anyway, this film has so many plot holes that it's not funny. It doesn't help that the mystery is practically non-existent, which means the film is padded with pointless scenes and dialogue. I'm still annoyed that I wasted two hours on this dumb film.