Cold-blooded (ectothermic) animals like reptiles cannot generate their own body heat internally. They must rely on external heat sources, primarily the sun, to warm their bodies and maintain metabolic functions. This is why lizards are often seen basking in sunlight. Unlike mammals (endothermic), they cannot regulate their body temperature internally. Option A is incorrect because cold-blooded refers to physiology, not emotions. Option C is wrong because their blood temperature changes with their environment.