I asked that Swedish creature...if it was bolted and she said it was

This quote, found in Chapter 4, Part two, is Mrs. Hubbard's undoing. Mrs. Hubbard tells Poirot that she had to ask Greta Ohlsson to check if the communicating door between she and Ratchett was bolted because her sponge bag was covering the lock. When Poirot enters Mrs. Hubbard's room to examine the weapon, he notices that the door bolt is one foot above the door handle. Mrs. Hubbard is caught in a lie that reveals her guilt. Until this moment, Mrs. Hubbard seems innocent, even a victim of the terrible murder next door to her, but this little lie implicates her in the crime.