"brr" gestures

Tom Clancy's Net Force: ONE IS THE LONELIEST NUMBER を読み始めました。主人公の一人（多分？）、Maj、が頻繁に出てくるのですが、正しい発音が分からないので、その分読むのが遅くなっていると感じます。　さて、早速興味の湧く表現が出てきました。
"We've got people out on the tarmac," Maj's duplicate suddenly said.
"Huh?" Maj was surprised at that. She had programmed her playroom to let her know with an audible chime when someone entered. She hitched herself up a little and peered over the edge of the cockpit. Roddy L'Officier was wandering around out there, hugging himself and generally making "brr" gestures.
最後に出てきた "brr" gestures とはどんなジェスチャーでしょうか？
・Wiktionary: An expression used to express being cold, to show shivering.
・Dictionary.com: interjection (used to express sensations of cold).
・Urban Dictionary: When its so cold that it makes you say "brr": John left the thermostat on cold overnight. When he woke up, he said brr.
日本語ではオノマトペのブルブルと似ていますね。但し英語の "brr" はバーに近い発音です。