This is not a voodoo ritual.
Scented soap under the mattress is a life hack used in Ritz-Carlton hotels.
Director of Services John Smith reveals secret to Travel + Leisure

"The scent of lavender or citrus improves the quality of sleep."
Scientists from the National Sleep Foundation have confirmed that light aromas reduce cortisol levels. Psychotherapist Emily Anders recommends in her book The Art of Rest :
"Choose a soap with vanilla notes - it evokes associations with childhood."
But in India, instead of soap, dried jasmine petals are placed under the bed, and in Japan, cedar shavings. A study by the University of Tokyo showed that natural scents shorten the REM phase of sleep, making rest deeper.
But there's a catch. Dermatologist Cheryl Carter warns in an article for Harper's Bazaar :
"Avoid synthetic perfumes. Only natural soap!"
And somnologist James Wilson adds in his book The Deep Sleep :
"The scents should be subtle. Too strong a smell can cause insomnia."
Put a piece under your mattress today and you'll wake up a different person tomorrow. Unless you eat it at night, of course.
And remember: the method only works with high-quality handmade soap. As Lush founder Mark Constantine says:
"Chemistry will never replace the power of nature."