Greek literature sometimes contains representations of animal cries in Greek letters. The most often quoted example is , used to render the cry of sheep, and is used as evidence that beta had a voiced bilabial plosive pronunciation and eta was a long open-mid front vowel. Onomatopoeic verbs such as for the lowing of cattle (cf. Latin '), for the roaring of lions (cf. Latin ') and as the name of the cuckoo (cf. Latin "") suggest an archaic pronunciation of long upsilon, before this vowel was fronted to .