system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What’s the scientific term for the tingling sensation (almost like a ground) that you feel when you say “gives me the chills”, and why does it happen?
gpt
It is technically called Piloerection! And it’s The same reason a dogs fur or spine-fur sticks out when it’s threatened, scared, or cold. The chills or goosebumps are typically a fear/excitement/body temp reaction. 

Back when humans used to be super hairy - when we’d be aroused, threatened, or cold, out hair follicles hardened, and continue to do so because of instinctual reaction to external stimuli. In fear or threatening situations - the hair follicles stiffen to make the hair stick and and appear bigger so that your enemy or threat will be more inclined to back off. In cold weather, your body does this to thicken the fur to disallow airflow and keep you warm. As far as excitement goes, like when you hear a good opera and you get chills - it’s because music that good can make you feel vulnerable, which circles back to fear. Your attention has become fixed on one thing for an extended amount of time, so now you’re aware or your surroundings suddenly and your hair puffs out to threaten other predators into thinking your bigger.