Second, SpriteKit uses a number of optimisations to help its physics simulation work at high speed. These objects, and our banana is just such a thing. To be sure everything works as intended, we're going to enable the usesPreciseCollisionDetection property for the banana's physics body. This works slower, but it's fine for occasional use.
第二，SpriteKit使用一系列的优化措施来帮助物理引擎模拟的高性能。这些优化措施对于小而快速移动的物体模拟的并不好，我们游戏中的香蕉炸弹就是这样的物体。
为了确保一切都工作正常，我们打算开启香蕉炸弹物理对象的usesPreciseCollisionDetection属性。这使得整个游戏引擎会变慢，但偶尔为之还是可以的 ；）
