(A) Video image showing the femur–tibia angle, femur–thorax angle and head–thorax angle that were analysed on six selected steps for song-left and song-right. Measures were taken for at least eight points with reference to the step cycle of the left front leg. (B) Change in femur–thorax angle during ipsilateral (Bi, left) and contralateral (Bii, right) acoustic stimulation. (C) Change in femur–tibia angle during ipsilateral (Ci, left) and contralateral (Cii, right) acoustic stimulation. Individual steps are indicated in red and the averages in black (top) or blue (bottom). AEP, anterior extreme position of the tarsus; PEP, posterior extreme position of the tarsus.