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Most scientific questions are based on observations.
Snail:
• They have a shell that is adapted to protect them against predators and the elements.
• They are also adapted to hibernate, especially snails that live in areas prone to frost or freezing temperatures, during the winters. Alternatively, snails in dry, arid regions will estivate - a summer version of hibernation - when water is scare or when there are droughts.
• Snails' slime is naturally hygroscopic, meaning that, instead of releasing water, it attracts it. This helps snails stay damp throughout the day and assists in movement, reproduction and breathing.
Crabs:
• Instead of having an internal skeleton they have exoskeletons. This creates an extremely hard exterior making them more susceptible to attacks from predators.
• All crabs have eight regular legs and two specially adapted legs known as chelipeds or claws. They help them to feed and to catch prey.
• All crabs have both a set of antennae and antennules. They see through their eyes, which are located on the end of long eyestalks. The purpose of these eyestalks is to allow them a better field of vision -- they can see in front of themselves, behind themselves and to the sides -- which is an advantage when hunting or looking out for danger.
Explanation:
While most snakes and lizards in North America are not poisonous, a few species can seriously injure or kill someone with their venom if the bite isn't treated quickly. They include the rattlesnake, copperhead, cottonmouth, coral snake, Gila monster, and Mexican bearded lizard.