He cocked his head curiously while listening to the teacher.

cocked 是动词 cock 的过去式。cock 本意是"竖起、抬起"，常用来描述动物竖起耳朵或人歪头、抬头的动作。这里 cocked his head 表示"歪着头"的动作，通常表达好奇或专注的状态。