Wear vintage clothes
For obvious reasons, when you are immortal, it means that you have lived for a long time. Therefore, when you want to make people believe that you are immortal, you have to show them that you have seen the cultures which have already died down. How can you make people believe it? You can wear older clothes. Just like in the usual vampire movies, you should try wearing old clothes and make people believe that you are not from the same point in time.
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When you are secretive, it means that there is something you know that the others do not know. This will make people want to know more about you. That way, with time, you will tell them some day that you are not from the current era; and in fact, you are not mortal and have been living for quite some time.
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Have an accent
People who used to live before us definitely had an accent. They used to speak proper English, but they always had an accent in order to reflect where they are from. If you develop an accent, you can make people believe that you are not from their area and have joined them from some other country or region.
Learn old languages
Learning an old language will help you in making others believe that you are not mortal. People before us used to know different languages and in order to make people believe that you are not from this world you have to learn another language. Try using a language-learning book as it will help you gain knowledge about older languages. A Greek language is something that will reflect that you are not from this era.
Use good vocabulary
Old aged people use better English and they never compromise on their accent. Therefore, in order to make people believe that you are not from this era and; in fact, are immortal, you have to start using proper English with a really good vocabulary. Now is the time to learn new words from your SAT books as they really help you going.
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