Leaning

Leaning, known as Contexual Lean in Call of Duty: Ghosts, is a mechanic in Call of Duty, Call of Duty: Classic and Call of Duty: Ghosts.

Call of Duty/Call of Duty: Classic
In Call of Duty: Classic, this can be activated by pressing the left and right arrow buttons. Pressing the left arrow button will make the character lean to the left, while the right arrow button will make the player lean to the right.

Call of Duty: Ghosts
In Call of Duty: Ghosts, this can be activated by going behind an object and pressing the aim button when a yellow arrow shows up next to the crosshair. Depending on what direction the arrow is pointing, the player will lean in that direction.