imperceptible

The change in the climate was so gradual as to be almost imperceptible.

(Chinese) 气候的变化是如此缓慢，以至于几乎察觉不到。

There was an imperceptible nod from the judge, indicating the hearing was over.

(Chinese) 法官微微点了一下头（几乎无法察觉），示意听证会结束了。