People have always been interested in animal communication and scientists have done a lot of research {#blank#}1{#/blank#} this subject. Most animals communicate by smell. Dogs are famous for this. When a dog walks outside, it learns about other dogs by {#blank#}2{#/blank#} (smell) things. Dogs {#blank#}3{#/blank#} (help) the police since a long time ago. Everyone has heard birds singing. Research has shown that many other animals use sounds {#blank#}4{#/blank#} (communicate). Frogs and insects communicate with sounds. Usually the "men" make sounds to invite the "{#blank#}5{#/blank#} (woman)". Whales and elephants {#blank#}6{#/blank#} use sounds to communicate. These sounds can travel very far through water or the ground. However, it is {#blank#}7{#/blank#} (possible) for humans to hear some of the sounds. They are {#blank#}8{#/blank#} too low or too high for us. Animals have always used body language to communicate as well. {#blank#}9{#/blank#} a dog puts its tail under its body, it is scared. When a dog wags its tail and {#blank#}10{#/blank#} (open) its mouth, it is happy.