A fox cannot hide its tail.; Evils cannot be covered up.
狐狸尾巴藏不住。
《新英汉大辞典》
2
The dog ran up, wagging its tail.
那条狗摇着尾巴跑上前去。
《牛津词典》
3
When the bear puts his tail into the water through a hole in the ice, to try and catch a fish, the ice freezes around it, and he ends up pulling his tail off.