Easter egg 
noun
1An artificial chocolate egg or decorated hard-boiled egg given at Easter.The chocolatier and confectioner spent long hours creating an enormous Easter egg, weighing in at 25 kgs of plain chocolate....
- The Mayor and her children are all partial to a good tasting chocolate Easter egg.
- As we wipe away the smudges of the last chocolate Easter egg, a pang of guilt associated with overindulgence might raise its head.
2An unexpected or undocumented feature in a piece of computer software or on a DVD, included as a joke or a bonus.The best thing about the game was finding the Easter egg....
- Also captivating are the various Easter eggs spread throughout the disc.
- Finally, there is a really funny Easter egg located in the upper right corner of the main menu.
- in the rough
- in the round
- in the saddle
- in the same (or next) breath
- in the second place
- in the sequel
- in the shape of
- in the shit
- in the short run (or term)
- in the soup
- in the swim
- in the teeth of
- in the throes of
- in the train of
- in the wake of
- in the wash
- in the way of
- in the whole (wide) world
- in the wings
- in the wink of an eye (or in a wink)
- in the works
- in the world
- in the wrong
- in the year of grace (or Our Lord) ——
- in this day and age