This also works on zombies. To use stealth, push and hold the crouch key (default key C on PC), or use Left Ctrl to toggle crouch mode. The crosshair will become an eye symbol and show whether or not the player is detected, hidden or sensed.
While crouched, certain actions are performed slower and quieter. For example, doors and storage are opened slower but quieter.
Zombies investigate sounds near them. Therefore, an item such as a Small Stone can be thrown to try to distract the zombie. Different actions have different noise levels. For example, a Chainsaw is louder than a Stone Axe and can more easily attract zombies.
Zombies are able to smell certain foods when carried by the player. This includes Bacon and Eggs, Raw Meat, and Meat Stew to name a few. Some foods like canned food have no smell but a fart from eating a Can of Chili will cause a detectable smell. Crouching has no effect on smells.
When a character is carrying something that smells, the Emitting Smell buff is activated and the smell icon25px becomes visible in the bottom-left corner of the screen as well as in the Character Menu.