otro gallo cantaría

The full phrase is "Si Pedro no hubiera negado a Jesucristo tres veces, otro gallo cantaría", meaning "if Peter hadn't denied Jesus three times, another cockerel would sing", in reference to the biblical story of the Denial of Peter.

otro gallo cantaría

1. woulda, coulda, shoulda; if pigs had wings they would fly; if my aunt had balls, she'd be my uncle

• harina de otro costal