Why is this the answer?

The answer is bull because this amazing riddle paints a perfect, detailed picture of a very strong animal that you would see on a farm. This puzzle uses imaginative words to describe the bull's features and its everyday life in its field. Let us look at all the hints one by one to see how they guide us to the correct answer. The riddle begins with a sound clue: a "muttered rumble was heard from the pen." Think about the deepest, rumbling sound an animal can make. That is the kind of noise a large male cow, or a bull, makes. The word "pen" is just another way to talk about the sturdy wooden fence that holds the animal in its field or barnyard. The next part describes the bull’s body. It calls the bull "A massive beast, hoofed, and jawed." Massive means the bull is super big and heavy, which we all know it is. Hoofed tells us it has hard feet like a cow, and jawed means it has a strong mouth. But the most exciting part is the line, "With spikes upon its mighty brow." "Brow" means forehead, and the "spikes" are a clever way to describe the bull's sharp, powerful horns! The riddle continues by showing us how the bull acts. It "struck the turf and prowled." When a bull gets excited or wants to show off its strength, it will often scrape the ground, which the riddle calls "turf," with its hooves. Prowled means to walk around slowly with great power, watching everything. Finally, we have the last line: "he couldn't get out of that wooden fence." This is a fun twist because even with all that power and magnificence, the bull is still safely kept inside by the farmer's strong wooden enclosure. This clever riddle tells the whole story of the mighty, powerful bull.