YOU SAID:

If his duck slap his thigh when he walk, I shall listen when he talk

INTO JAPANESE

彼が歩いているときに彼のアヒルが彼の太ももを叩いたら、私は彼が話すときに耳を傾けます

BACK INTO ENGLISH

If his duck hits his thigh when he walks, I listen when he speaks

INTO JAPANESE

彼が歩いているときに彼のアヒルが彼の太ももにぶつかった場合、私は彼が話すときに耳を傾けます

BACK INTO ENGLISH

If his duck hits his thigh when he walks, I listen when he speaks