"not what you think"
A rooster
GNU Free Documentation LicenseA rooster - Credit: Muhammad Mahdi Karim

A rooster crowing is traditionally a sign of infidelity.

This comes from the biblical story of Peter's denial of Jesus on the night before he is crucified. Shortly before he is arrested, Jesus tells Peter that no matter how loyal he feels to him, he will have betrayed him three times by the time the cock crows the next morning. Peter is sure it isn't true, yet when the crowd turns against him Peter finds himself denying that he knows Jesus three times. As soon as he has uttered the third denial, the cock crows and Peter realises what he has done.