Is it possible to alter a persons feeling or thoughts? See details...?

One of my friend is afraid that someone would influence/change his feeling(vision/hearing etc) or even his mind sometimes. For example, one day he got something strange into his eyes, and he doubt if some material could cause illusion or hallucination. For another instance, one day some suspecious men walk by... show more One of my friend is afraid that someone would influence/change his feeling(vision/hearing etc) or even his mind sometimes.

For example, one day he got something strange into his eyes, and he doubt if some material could cause illusion or hallucination.

For another instance, one day some suspecious men walk by him, then he feel itch on his eye, he swipe his itch eye and found something like a dead insect on his hand. He doubt if it s just a coincidence, or it s something those people designed to put to his eye.

Many people think he has mental problem, but I know his story/history and I agree he do have a valid reason to worry, I just cannot share it here.

My question is: Is it technically possible to influence or even emulate a person s feeling or mind without installing heavy devices on him, just do it secretly?

Sorry for my non-native English.
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