You must have a Ninjitsu skill of 50 or higher before you can use egg bombs. When you do so, a Hiding skill check is performed and if it is successful you are hidden no matter what.
This counts as activating the Hiding skill and is thus affected by skill delay. Also if you are revealed you cannot use an egg bomb to hide again at once - A period of time equal to the that of the skill delay will have to pass before you can detonate another.
Crafting
Cooking
Note: Only one Sack of Flour is even partly used, but you must hold three and all three must be open.
Alchemy