Little balls in wooden tracks are really susceptible to humidity and temperature and a little bit of dust, and they fall out of the tracks, the exact angles makes it hard to get right.
那些木制轨道上的小珠子 非常容易受 湿气，温度，和哪怕一点灰尘的影响。 它们从轨道上滚落 很难把握角度的精准度。