I never wear flip flops because I have to grip them tight with my toes to prevent them falling off, and then I have to shuffle in order to not lose them. Flip flops are horrible in my case. But I wear sandals. And yes, the feeling of sand under my feet makes me feel extremely nauseous. I have hypersensitive touch, especially on my feet. So I can relate.
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I am a partially verbal classic autistic. I am a pharmacology student with full time support.