Jeff feels his clothes fall away as he shrinks, his body flattens, his legs shrink away and vanish, his private parts dematerialize, his head contracts into his chest and his arms vanish, as his form flattens and three holes appear in the silky lacy cloth.
Mom looks at the pair of lacy red panties sitting where her son had been, laughing in a mixture of amusement and malice. Jeff is still aware of his surroundings, he's aware as his mother takes off her flip-flops and slides her jeans down, and then takes of her boring underwear. Jeff can't believe it as his mother puts him on, sliding her still-nice legs through his silky form, and letting him come to rest against her butt and crotch.
"Wow, this is so twisted!" Mom says with a giggle. "How does it feel to be my panties, son?"
It felt strange, embarrassing, and at the same time kind of exicting...