Uma Thurman at Room to Grow 10th Anniversary Benefit Gala held at Christie's, New York City, USA - 02.12.08

The 38-year-old Kill Bill star unbuckled her seat belt and started stretching during a flight from New York to Salt Lake City, Utah, where she will appear at the Sundance Film Festival this weekend (beg17Jan09).

A witness tells the New York Post, "She used the flight-attendant station as a ballet barre, where she stretched and did plies for 20 minutes."

But the in-flight antics were the end of Thurman's health-consciousness, according to the onlooker: "After we left the plane, she ran for an exit and then chain-smoked like crazy."

Source: WENN