Nicole Kidman beat Aniston in a "hula dance-off" in Hawaii
The Hollywood beauties are currently filming upcoming romantic comedy `Just Go With It` on the island of Maui, and they can`t stop "goofing off" on set and even challenged each other to an exotic dance competition involving hula hoops - which, after a close battle, was eventually won by Nicole.
A set source said: "They are totally bonding together and look like absolute best friends, hanging out between takes, laughing, joking and goofing off together.
"Friday was absolutely hilarious, the two of them decided to have a hula dance-off competition. We all had to judge who was the best hula dancer, and they performed for like five minutes each. They were both amazing and it was declared a tie, but they wouldn`t accept that ruling and both insisted on going another round, this time with a hula hoop! Nic just managed to pip Jen to the post, keeping going for around 30 seconds more. It was a tight one, but she just won by the skin of her teeth!"
The pair have kept this light-hearted approach to their work up throughout filming, and fellow cast and crew are amazed by how well they have bonded.
The source added to RadarOnline.com: "That`s completely what filming has been like the whole time, just fun and games, it`s amazing.
"This has to be one of the most fun film sets I-ve ever been on, and I`m sure that`s going to come over on the finished movie.
"Both Jen and Nic are absolutely awesome. They are totally down to earth and really approachable and friendly."
`Just Go With It` stars Adam Sandler as a plastic surgeon called Patrick who is so afraid of commitment he tells his young girlfriend Beverly, portrayed by model Brooklyn Decker, he is already married.
Jennifer will play his fake wife Palmer, while Nicole stars as Rea Ann Devlin.
Nicole, 42, and 41-year-old Jennifer have been getting on so well, they have even started offering each other fashion advice.
The source added: "It was so sweet, they were just like two regular girlfriends shopping together!"