This is an animation example.  and here is the code:
 

bg 409
robot 1 [on speed = 20 dir = 45]
robot 2 [ on speed = 30 dir =  -45 rgt 100 0 ]

robot 1 [
animate 0.2 [
shapewh 125 50 [color white a]
 shapewh 125 50 [color white b]]
]
robot 2 [
animate 0.1 [
shapewh 125 50 [color white a]
shapewh 125 50 [color white  b]]
]
song "flying bird2 song.mp3"  //The files needs to be in the same directory

The code for a is:
mirror  [
 LT 270 CURVEl 80  60 RT 270
jt 0 0 ]

and for b:

mirror  [
 LT 290 CURVEl 80  60 RT 290
jt 0 0 ]