People already know a lot about animals. However, there are still some things about animals that may surprise you. Here are some facts about animals you probably didn’t know.

　　Cows do have best friends and feel stressed when they are separated. Scientists have found that cows are very social animals and a cow always makes friends with other cows. When a cow is with its friends, it feels relaxed, compared with when it is alone.

　　During breeding season, a male penguin (企鹅) will offer a small stone to a female penguin as a gift. If she takes it, they will become partners. When the female penguin lays an egg, she and her partner may carry it on their feet, because some penguins don’t build nests (鸟巢).

　　Crocodiles (鳄鱼) swallow (吞) stones. Crocodiles always swallow their food instead of eating it like other animals. They swallow stones which break the food into very small pieces in their stomachs. These stones may stay in their stomachs all their lives.

　　Elephants use plants to treat pain or other illness. Scientists once found a pregnant (怀孕的) elephant in Africa who ate a kind of plant which was not part of her normal food. Four days later, she gave birth to a baby elephant. The same plant was used by the local pregnant women.