Like many languages , English uses animals in many of its expressions . And there are thousands of kinds of animals . So , when we talk about them , we put them into different groups . Take , for example , pack animals . One kind is an animal used to carry packs , or heavy loads . Donkeys and mules are pack animals . We sometimes call these animals beasts of burden because they help to ease the burden of humans . Another type of pack animals are the ones that live and hunt in a group , or pack . These include grey wolves and dolphins , just to name a couple . Running with a pack has many benefits . When animals live in a pack , they work together . There is strength (and safety ) in numbers . If you run with a pack , you can depend on others in your group . And there is always someone who has your back , or is ready to fight for you . We can describe people the same way . Some like to run with a pack . They like to surround themselves with like-minded people . People can run with a pack that likes the same music , has the same politics or enjoys the same activities . It is easy to hang out with people who generally agree with you . It is comfortable -- maybe a little too comfortable . This can lead to a pack mentality , a situation where everyone thinks the same . After time you could become resistant to ever disagreeing , fearful of losing your place in the pack . We also call this groupthink . This is a situation where members of a group feel pressure to always agree . Groupthink results in failures to think critically about an issue , situation or decision . Groupthink or pack mentality can even be dangerous . People caught up in a pack mentality do not think for themselves and can make bad decisions . So , parents often try to control which pack their child runs with . With both animals and people , there is usually a leader of the pack . In our human pack , the leader is the one who calls the shots . They make the decisions for the group . Some people , however , have no desire to run with a pack . They might be ahead of the pack and are more forward thinking . They do not want to go along with what everyone else is doing . Maybe they are just faster ! Or perhaps they simply enjoy the life of a lone wolf . As a lone wolf you solve problems by yourself . You do not ask for help when making decisions . You are free from pleasing a group . However , you might not have many friends . After all , everything has a cost . Now , we finish our show with yet another type of pack animal – the pack rat . This is a small rodent of western North America . Pack rats have large cheek pouches , where they store food and other things . These pouches can fill up fast ! In the human world , pack rats are people who keep things that they do not need . They store them , not in their cheeks , but in their homes , garages and other storage places . A pack rat often says things like , “I can't throw it out . When pack rats collect too much stuff and it interferes with their life -- they have become a hoarder . Hoarders have a difficult time throwing anything away . So , they usually find themselves surrounded by stuff , sometimes even buried under it ! However , sometimes it pays to be a pack rat or at least to know one . One day you just may need something they have collected – a 40-year-old newspaper , a bicycle wheel , or a cow bell . One look in a pack rat's basement or garage and you just might find what you need !