[Something] as a(n) [animal].

[vakkotaur]

Not sure what brought this on, but here it is.

Blind as a... bat
Busy as a... bee
Free as a... bird
Happy as a... clam
Healthy as a... horse
Hungry as a... bear
Hungry as a... horse
Mad as a... wet hen
Naked as a... jaybird
Proud as a... peacock
Sick as a... dog
Silly as a... goose (not a turkle?)
Sly as a... fox
Strong as an... ox
Stubborn as a... mule

Not that these are really accurate, merely in common(?) use.