Does Latin, particularly Classical Latin, have a similar synonym for coward, comparing a cowardly person to an animal of some kind? Wiktionary doesn't mention one, and I don't see one in Wikipedia's list of Latin phrases either.
I always liked Horace's simile comparing Chloe to a fawn in Odes 1.23:
Vitas hinnuleo me similis, Chloe,
quaerenti pavidam montibus aviis
matrem non sine vano
aurarum et siluae metu.
nam seu mobilibus veris inhorruit
adventus foliis seu virides rubum
et corde et genibus tremit.
atqui non ego te tigris ut aspera
Gaetulusve leo frangere persequor: tandem desine matrem
tempestiva sequi viro.
English taken from Wikisource:
You avoid me like a deer, Chloe,
seeking its trembling mother in the remote mountains
not without an empty fear
of the winds and the forest.
For whether the arrival of spring quivered
with shifting leaves, or whether green lizards
have moved a bramble,
it trembles with both its heart and its knees.
Nevertheless I do not pursue you, as a cruel tiger
or as a Gaetulian lion, to break you:
Cease to follow your mother—
at last you are ready for a man.