Final answer:
The information about Dr. Roylett's love for Indian animals is crucial as it foreshadows the use of a venomous Indian snake as the murder weapon in 'The Adventure of the Speckled Band'.
Step-by-step explanation:
The author of "The Adventure of the Speckled Band" gives an important clue about Dr. Roylett's preference for exotic animals from India which becomes crucial for solving the murder mystery.
This detail is significant because it ties directly to the method of murder used in the story. The speckled band turns out to be a venomous snake from India which Dr. Roylett has been keeping as a pet. He uses the snake as a weapon to carry out the murder, and its identity is concealed by the strange symptoms of the victim's death.
This unusual choice of murder weapon highlights Sherlock Holmes's attention to seemingly trivial details that are often overlooked by others but are vital in his method of deduction.