Final answer:
Richard Parker, the tiger, might be conserving energy or not in urgent need of food, which explains his quiet observation rather than attacking the zebra himself. His behavior can also be affected by the peculiar situation of being on a lifeboat.
Step-by-step explanation:
The question pertains to the behavior of the tiger named Richard Parker in a situation where a zebra is vulnerable and is being attacked by a hyena. It is probable that Richard Parker is assessing the situation or is not in immediate need for food, which is why he does not take an opportunity to kill the zebra himself. Big cats, such as tigers, are known to be strategic hunters, and they may choose to conserve energy if they do not feel the urgency to eat or if they are observing the dynamics of other predators and prey in their vicinity. Additionally, Richard Parker's behavior might also be influenced by the unusual circumstances of being on a lifeboat, potentially altering his natural instincts.