Final answer:
Abby means that one should carefully investigate and analyze the condition of the animal to help it, akin to detective work.
Step-by-step explanation:
When Abby (Lilli) compares helping someone to helping a sick animal by saying, "You have to sleuth for the animal!" she means that one must Examine thoroughly. The term 'sleuth' refers to investigating or solving something with keen attention to details, similar to what a detective would do. In this context, Abby implies that one should carefully observe and analyze the condition of the animal to determine the best way to help it, which requires patience and attention to detail.