Some snakes harm their prey by injecting venom through their fangs; some of this venom can be harmful to humans, resulting in what we often think of as "poisoning" (although it's technically called venom, not poison). It is not out of the question to encounter snakes while hiking or camping. So, before venturing into nature, it's necessary to know how to tell the difference between venomous and non-venomous snakes.

PART ONE Identifying Common Features;

1. Look at the head. Most venomous snakes have triangular shaped heads, though not all. This is a good rule of thumb, but it does have exceptions.

2. Observe the colors. Some venomous snakes such as the coral snake have bright colors.

3. Many people will try to judge if a snake is venomous by looking into its eyes.This is ineffective, because the information you gain from this observation only tells you what time of day the snake is active. Snakes that are nocturnal (hunt during the night) generally have slitted pupils, while snakes that are diurnal (hunt during the day) generally have round pupils. Some of the most venomous snakes in the world have round pupils, but many infamous snakes such as rattlesnakes have the classic slitted pupil.

4. Look for a pit between the snake's eyes and nostrils. A venomous snake normally has a heat-sensitive pit there to locate warm-blooded prey. Non-venomous snakes lack such pits.

5. See if there is a rattle. A snake with a rattle on its tail must be a rattlesnake, which is venomous. The Florida Pygmy Rattlesnake often only has one segment of rattle and thus cannot make a warning noise.

6. Notice the underside scales on the tip of the tail. Most venomous snakes have one row of scales there while non-venomous snakes usually have two rows.

7. Check the bottom of the tail if you can. The bottom of the tail (behind the anus) of venomous snakes looks the same as the rest of the belly. If the snake has a cross pattern (like a diamond shape) it is non-venomous. However, this may not be easy to find out, unless the snake is dead.

8. Watch water snakes swim. Only venomous water snakes swim with their entire bodies visible on the water.

9. Examine the bite marks in case of a snake attack. Two close-set puncture marks would indicate that the snake has fangs and is venomous. By contrast, a ragged bite mark means the snake lacks fangs which is a characteristic only of non venomous snakes. There are exceptions here, like coral snake bites, but this is a decent rule of thumb.

PART TWO Knowing the Exceptions

Look out for the exceptions to the rules above:

• The coral snake is venomous but has a round-shaped head while some non-venomous snakes may flatten their heads to resemble triangles when they are threatened.

• Some colorful snakes, such as the scarlet snakes, the scarlet kingsnake, and the red milk snake, are non-venomous.

• The black mamba, the coral snake, the cobra, and the inland taipan snake are venomous but have round pupils. Pupil shape has nothing to do with whether a snake is venomous or not - but it does tell you when the snake likes to be awake!