Final answer:
Without the context of the literary work being referenced, it is not possible to determine what Alex tells the guests at Christiane's birthday celebration. The provided excerpts suggest a dramatic moment but do not offer specifics.
Step-by-step explanation:
The specific details of the student's question, referring to what Alex tells the guests at Christiane's birthday celebration, cannot be answered without additional context. This sounds like it could be a question about a particular book, play, or other piece of literature. As the provided information does not give the name of the work or the author, it is impossible to determine what Alex said. Typically, Alex's comments would reveal crucial information about the plot or the relationships between characters that could shift the mood of the celebration.