as stubborn as ...
a mule
as graceful as ...
a swan
as quiet as ....
a mouse
as slow as ...
a snail
as watchful as ...
a hawk
as sly as ....
a fox
as free as ...
a bird
as dumb as ....
an oyster
as blind as ...
a bat
as hungry as ...
a wolf / a bear
as wise as ...
an owl
as strong as ...
a horse / a bull / an ox