What you can bring on a plane

Because the rule is about who can put out a fire. A lithium cell that goes into thermal runaway in the cabin is noticed within seconds and dealt with by the crew, who carry equipment for exactly this. The same cell in the hold burns unseen for as long as it takes, and nobody can reach it in flight. So the counterintuitive answer is the safe one, and it is the single most common reason bags are opened at the belt.

At screening, yes. The rule covers anything that can be poured or spread — gels, pastes, creams, honey, jam, yoghurt, soft cheese, soup. That is why food is taken from travelers who never thought of it as a liquid: a 250 gram jar of honey is a 250 milliliter container, and the cabin limit is 100. Hard cheese and chocolate are solid and raise no question.

The rules of the country whose airport you are being screened in, and screening happens again at the transfer. A duty-free bottle bought legally in one country can be taken at the next checkpoint if the sealed bag has been opened or is not recognized there. This is why the tool asks you which jurisdiction you are reading rather than guessing once and hiding it.

For ordinary items — scissors, a full bottle, a lighter in the hold — the item is surrendered and you fly. For weapons, undeclared firearms, ammunition and cannabis products, it stops being a confiscation and becomes a matter for the police, with consequences that depend on the country rather than the airline. The difference is worth knowing before you pack, not at the belt.

Yes, and they have been for many years, in the cabin, in every jurisdiction listed here. It is one of the most persistent myths in the field. Sharp items are judged by blade, and a knitting needle has none; a corkscrew with a foil knife, which looks far more innocent, is the one that gets refused.

Yes, in both bags and without a quantity limit, and liquid medicines are exempt from the 100 ml rule in the amount you need for the trip. Keep them in the original packaging with the pharmacy label and declare them at screening. The harder question is the destination: some medicines that are ordinary at home are controlled or banned on arrival, and that is customs law rather than aviation security.