Germany's Auto Motor und Sport reports that mechanics working for the Brackley based team are making more efforts than usual to hide the front and rear of the car, and erecting huge screens in front of the pits between test runs in Barcelona.
But a big secret is now out of the bag, and it's located beneath the rear rain light and being described by insiders as "like a double diffuser".
Italy's La Gazzetta dello Sport said the feature is believed to produce an effect similar to the one pioneered by Mercedes' predecessor Brawn GP in 2009, which resulted in the championship for Jenson Button.
And according to Auto Motor und Sport, the concept differs to the banned double diffuser because the air is channelled through holes at the rear of the engine cover.
The concept, despite complying with the FIA's blown diffuser clampdown, also reportedly involves the clever redirection of exhaust gases.
And yet another innovation on the Mercedes could be a passive 'F-duct'-style addition to the car's new rear wing, working alongside the 'DRS' system.
When asked about the 'ducts', Rosberg and Schumacher played it coy: "What's that?" Rosberg answered, while Schumacher joked that it sounds like something that should go "quack!"
"They are a good team," Red Bull team boss Christian Horner told Sky when asked about Mercedes.
"They have some good people so it would be foolish to underestimate them."
Meanwhile, TZ newspaper in Germany reports that the FIA could be set to clamp down even harder in the area of exhaust blowing.
There are rumours Renault and Mercedes-powered teams are still using clever engine mapping techniques for aerodynamic effect.