a sop to Cerberus

A bribe. Taken from the ancient Greek and Roman custom of leaving gifts with corpses so that Cerberus (guardian of the gates of hell) would pass them by. What is this money, a sop to Cerberus so that I won't tell the authorities what you've done? Of course we can get the city council to approve of our plan. All we need is a sop to Cerberus. You know, a sop to Cerberus might help me to remember a few details about the people you're asking about.

a sop to Cerberus

something offered to appease someone.

In Greek mythology, Cerberus was the three-headed watchdog which guarded the entrance of Hades. In the Aeneid Virgil describes how the Sibyl guiding Aeneas to the underworld threw a drugged cake to Cerberus, thus enabling the hero to pass the monster in safety.