Step-by-step explanation:
The effect of epinephrine is that it is what is responsible for making his pulse raise.
Epinephrine is what is commonly called adrenaline. Increased pulse rate is an effect of adrenaline rush in the bloodstream.
The peripheral nervous system passes information to the brain. It is what made him to tighten his grip on the leash involuntarily.
The occipital lobe is what helps to process vision. Brandon tried squinting in order to focus on what caused the dog to be at alert.
Natural selection is how people or living things try to adapt to changes. The dog starts to growl due to the changes that it observes in the environment.