What is hidden in 3D image?

A guy goes into a bar. He's sitting on the stool, enjoying his drink when he hears, "You look great!" He looks around - there's nobody near him. He hears the voice again, "No really, you look terrific."

The guy looks around again. Nobody. He hears, "Is that a new shirt or something? Because you are absolutely glowing!" He then realizes that the voice is coming from a dish of nuts on the bar.

"Hey," the guy calls to the bartender, "What's with the nuts?"

"Oh," the bartender answers, "They're complimentary."