Fill a medium saucepan with ½ cup water, bring to a gentle boil, and place a heatproof bowl over it to create a bain-marie.
Add butter and marshmallows to the bowl and melt slowly, whisking until smooth and glossy.
Remove from heat, whisk in salt and 2-3 drops of red food coloring.
Pour the marshmallow mixture over Rice Krispies and stir quickly to coat evenly.
Oil your hands, shape portions into oval brain forms, and carve a groove down the center with a butter knife.
Use a toothpick dipped in food coloring to draw realistic vein patterns for a spooky effect.