It's your body reacting to the core temperature dropping. Muscles generate heat when they're used - that's why you sweat when you work out - so by twitching the muscles your body can warm itself.
No they do not. that's what there shell is for. it makes it so its not cold.
no penguins do not shiver they never never ever get cold
it was so cold even the dog started to shiver
to sheever
chatter or cold
They shiver
it is when you are cold or you are hunger
it is because of a biological change in body temperature which causes your muscles to get warmer and not cold.
shivering is said to warm your body when cold.
A cold shiver ran down my spine at the dead of night.
its cold
Shiver, chatter