A man was walking on one side of a river, his dog on the other. When he called his dog, she came to him and he hugged her.
But how she crossed the river without getting wet and without using a bridge or a boat or without taking any help.
ANSWER;
River is frozen.
This is one of the most known riddle and good example to the question, What is an example of a brain teaser?
Brain Teaser Questions 