What means the simile "Stops and curl up like a chestnut burr"?

i need to know what does this simile means...please help :))

What means the simile "Stops and curl up like a chestnut burr"?
"You are like a chestnut burr, prickly outside, but silky-soft within, and a sweet kernel, if one can only get at it"



Little Women

by Louisa May Alcott



"like a chestnut burr" is the term, and in your poem the hedgehog ends up looking like a chestnut because he

curls up in a ball



Church is like a chestnut burr : the burr is one, but there are two nuts, and sometimes three, inside of it !



Mostly 19th century,