Each body paragraph is something like a miniature essay in that they each need an introductory sentence that sounds important and interesting, and that they each need a good closing sentence in order to produce a smooth transition between one point and the next. It depends on the idea you want to develop in your paragraph.
Depending on the specific style of the essay, you may be able use very short paragraphs to signal a change of subject or to explain how the rest of the essay is organized. Providing extensive background may interest some readers, but others would find it tiresome.
You can also begin with a sentence on means of protection, dogs being an example of a good way to stay safe.
The context is the starting point for your introductory paragraph. Once the starting point and ending point are determined, it will be much easier to connect these points with the narrative of the opening paragraph.
They will enter and depart from our existences as matters of mutual convenience. This shaped the topic and narrowed the focus to dogs as friends.
This would make writing the remainder of the essay much easier because it allows the writer to focus on aspects of dogs that make them good friends. If the thesis contains multiple points or assertions, each body paragraph should support or justify them, preferably in the order the assertions originally stated in the thesis.
The writer may next ask what characteristics dogs have that make them true friends.
Each characteristic may be the topic of a body paragraph.
For example, a thesis might read: You are telling the reader what you think are the most important points which need to be addressed in your essay.
For this reason, you need to relate the introduction directly to the question or topic.