Let's say you have a planet rigged to explode only if two bowling balls hit respective sensors at the same time. An unfortunate observer, call him Carl, releases two bowling balls at the same time from his reference frame. Meanwhile, Shirley passes by at nearly the speed of light. From Shirley's perspective, the bowling balls do not hit the sensors at the same time. However, since the sensors and the explosives share a reference frame with Carl and his simultaneous release, the planet explodes. Does Shirley observe the non-simultaneous bowling ball impacts followed by the planet (paradoxically) exploding?