Hi! I am also familiar with this. In some provinces here it is believed that giving a knife as a gift to a friend will "cut" the relationship. Therefore, those who receive it, give back a coin (of little value) used to symbolically pay the gift received. Sometimes, for this reason, the one who gives a knife as a present includes a coin, so that those who receive it, can return the same as "payment".
In other provinces, stirring liquids or powders with a knife is considered to bring bad luck, hence the rhyme which reads: "Stir with a knife, dispute to come". In some alpine provinces instead, giving a knife is considered a sign of respect and trust. The knife is given always unpacked (but can be with a sheat), holding out the handle to the receiver, to symbolize trust and friendly intentions.
Some people I met believe passing a switchblade with the blade open to anyone will bring bad luck.
Also someone believes that closing the blade of a folder that someone else had opened, will bring bad luck. I even heard people who are convinced its bad luck to open (or unsheathe) a knife without using it.
Some believe that a knife does not belong to an individual until this has hurt him. Those who believe in this superstition consciously prick a finger on the blade in order to avoid the risk of cutting badly accidentally later on.
Also here it is commonly believed that eating the food from the knife blade, instead from a fork or a spoon (or otherwise bring the knife to the mouth) will bring bad luck (and considered rude nevertheless). Superstitions are somehow interesting to explore and understand
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