Listen closely for unabashed giggling.

（友人が周りの目を気にせず笑い声をあげているのを耳を澄まして聴きましょう。）
　最近購入した本『Balance--a guide to life's forgotten pleasures』（邦題：『人生をひそかに楽しむための45の方法』）より、人生をひそかに楽しむためのHow toのひとつ「How to give a piggyback ride」より。

• listenのあとがtoじゃないことが気になって調べてみた。すると"listen for something"で「特定の音を聴くために気をつけて耳を澄ませる、聞こうとする（to listen carefully so that you will notice a particular sound／make an effort to hear something／be alert and ready to hear something) 」という意味だった。
  • I will have to let you in the front door if you come home late. I will listen for you.
  • I am listening for the telephone.
  • They listened for sounds from the baby's room.
  • Listen for the moment when the music changes.
• piggyback (ride)は「おんぶ、肩車」のこと。unabashedは「恥ずかしがらずに／臆面もなく」。
• How to give a piggyback ride
  1. Convince friend to abandon pride and hop onto your back. (Fig1: a standing woman and a man who is bending forward)
  2. Have friend hold on to shoulders--not hair, head, or ears. (Fig2: a woman is piggybacking on a man)
  3. Run around. Listen closely for unabashed giggling. (Fig3: a man giving a piggyback ride is running around)