Sentence 1: Bob walked into the ship elevator and heard a voice on the speaker. 
 Sentence 3: They were surprised to hear the voice in the hallway to their cabin 
 Sentence 4:  The voice could still be in their cabin, so they called the steward 
 Sentence 5:  The steward found that the voice was coming from Bob's pocket phone 
 Given Sentence 2: Whenever he doesn't have coffee, he gets a slight headache.