the.com/shiver
your body's involuntary attempt to start a fire by shaking very, very hard
means To shake or tremble slightly, usually from cold, fear, or excitement.
from From Middle English chiveren, possibly an alteration of an earlier word related to the chattering of teeth — the sound the body makes when it can't hold still. It's tangled in the family of trembling words (shudder, shake) where the meaning practically rattles on the tongue. Note the nautical 'shiver me timbers' is a different cousin: there 'shiver' means to splinter or break apart, from a separate Germanic root meaning a sliver or fragment.
how it worksMuscles spasm rapidly to generate body heat
the goosebumpsTiny muscles raise hairs to trap warm air
fever twistYou shiver when feverish to raise temperature higher
not just coldFear and emotion trigger the same reflex
old wordRooted in a term meaning to splinter or fragment