When a snake sticks its tongue out it is just trying to get to know you by capturing your body smells and transmitting them to its Jacobson organ. The Jacobson organ located in the roof of the mouth allows the snake to decide whether you are prey, predator or mate. Again nothing to worry about. Snakes play a critical role in the environments where they occur, primarily by the position they hold in the food chain or ecosystem. In the rural areas of Hong Kong, snakes serve a highly useful purpose because they feed on cockroaches, flies, grasshoppers and rodents such as rats and mice.
Many snakes are top-level predators.
For example, a single rat snake can consume more than 100 rodents a year. Others are important in the control they exert on insect and other invertebrate populations. All snakes form part of the diet of other predators, including several species of snakes, birds of prey and various mammals, and thereby serve to link higher and lower feeding levels. Hong Kong's snakes have highly specialised feeding habits. Some species eat chiefly snails.