Here is a great scene from (near the end of) the film Arsenic and Old Lace. To help the scene makes more sense, the wine in the sceen is poisoned but the two villians don't know.
PLOT: (supplied by wikipedia)
A drama critic and confirmed bachelor, Mortimer Brewster (Cary Grant), has written a number of books describing marriage as just an old-fashioned superstition. Nevertheless, he falls in love with and marries Elaine Harper (Priscilla Lane), who grew up next door to his old family home in Brooklyn.
Immediately after the marriage, he visits the bizarre relatives who still live there, two elderly aunts (Josephine Hull, Jean Adair) and his brother Teddy (John Alexander). Teddy thinks he's Theodore_Roosevelt; each time he goes upstairs he blows a bugle, yells "Charge!", and takes the stairs at a run (in imitation of Roosevelt's famous charge up San Juan Hill. Mortimer finds a corpse hidden in a window seat, and tells his aunts that Teddy must be sent to an asylum, as he has killed someone.
At this point, Mortimer's sweet, if misguided, aunts explain that they are responsible ("It's one of our charities"). They have developed what Mortimer calls the "very bad habit" of ending the presumed suffering of lonely old bachelors by serving them elderberry wine spiked with arsenic strychnine, and "just a pinch of cyanide". The bodies are buried in the basement by Teddy, who thinks he is digging locks for the Panama Canal and burying yellow fever victims.
To complicate matters further, Mortimer's other brother, Jonathan (Raymond Massey), arrives with his alcoholic accomplice, plastic surgeon Dr. Herman Einstein (played by Peter Lorre, and loosely based on gangland surgeon Joseph Moran), in tow. Jonathan is a vicious multiple murderer whose face, as altered by Einstein while drunk, resembles that of Boris Karloff in his makeup as Frankenstein's monster. This comparison is frequently noted in the film, much to Jonathan's annoyance. (This was originally a self-referential joke, as Karloff himself had played the character in the stage production). Jonathan, upon finding out his aunts' secret, decides to bury his own murder victims in the cellar (to which Abby and Martha object vehemently, because their victims were all nice gentlemen) and soon declares his intention to kill Mortimer.
Mortimer makes increasingly frantic attempts to stay on top of the situation as his bride waits for him next door, including multiple efforts to alert the bumbling local cops to the threat Jonathan poses to society. He worries whether he will go insane like the rest of his family. But eventually Jonathan is arrested, while Teddy and the two aunts are safely consigned to an asylum. In the end, Mortimer is overjoyed to learn that he was adopted and is not biologically related to the Brewsters after all. He is actually the son of a sea cook (in the original play, he happily tells Elaine that he's a bastard).