Motion on the web can cause real harm if not designed carefully. Certain animations, such as large-scale movements, parallax effects, or rapid flashing, can trigger issues for users with vestibular disorders, migraines, or epilepsy. While guidelines like WCAG 2.2 address some of these risks, they often focus on reactive measures rather than preventive strategies. The author emphasizes the need for animations to "fail safely," which means they should stop gracefully without causing additional distress when something goes wrong. To achieve this, the article introduces a framework called defensive animation design, which incorporates principles from defensive programming. Key tactics include setting time limits on animations to prevent them from running indefinitely, implementing circuit breakers to halt abnormal behavior, and providing non-animated fallback options so users can still understand what's happening when things fail. Monitoring user patterns and consolidating competing animations can help avoid overwhelming experiences. For instance, using tools like PerformanceObserver or IntersectionObserver can help manage resource use and prevent chaotic visual overload. The framework also stresses the importance of coordination in animations. By tracking the state of active animations, designers can avoid overlaps that might confuse users. This approach creates a safer, more predictable experience. Overall, defensive animation design aims to protect users from harmful effects while maintaining the engaging qualities of motion in web interfaces.