NEW YORK — It'll never rank up there with turkey and pumpkin pie, but for millions of Americans the Thanksgiving experience just wouldn't be the same without ... helium. For 364 days of the year, the colorless and odorless gas works quietly behind the scenes, doing jobs like chilling magnets in MRI imaging machines and helping welders protect their work from impurities. But on Thanksgiving, the lighter-than-air element moves onto a much bigger stage.