An intriguing Easter egg has been discovered in Batman: Arkham City: Big Head Mode.

Big Head Mode is activated by holding down LT and RT on 360, or all four shoulder buttons on PS3, and rotating the left and right analogue sticks in opposite directions for five seconds.

This gives everybody - including enemies, playable characters, and the game's DLC outfits - a massive head, just like in games you used to play in the glorious olden days.

There are a couple of reported caveats, however: you can't do it on Easy mode, and you're required to have completed the game at least once before the cheat will work.

Batman: Arkham City developer Rocksteady has a history of peppering their games with Easter eggs, and it's likely there's more hidden within the walls of Hugo Strange's giant penitentiary: nobody found Warden Sharp's hidden room in Batman: Arkham Asylum until Rocksteady basically told everybody where it was, for instance.

"Rocksteady has created an intricate, spirited and unequalled playground worthy of one of the most iconic characters in modern fiction," wrote VideoGamer.com in its 10/10 Batman: Arkham City review.

Carry on the conversation on the VideoGamer forums!