MEXICO CITY (AP) — Somewhat predictably, an attempt by three people to smuggle two howler monkeys in southern Mexico was undone when the protected animals locked in a suitcase began emitting their piercing cries.

The National Guard said Wednesday that officers uncovered the smuggling try when they stopped a car for a traffic infraction near the Bacalar lagoon close to the Caribbean coast and heard “strange noises” coming from the suitcase.

Howler monkeys are known for a deep, barking roar and in the wild they are usually heard long before they are seen.

They are a protected species and transporting them is illegal without proper licenses. The monkeys were handed over to environmental authorities, and the three suspects were turned over to prosecutors.