When a skeleton is inside of it's target his head faces down and he can't attack.

Also if the target jumps the skeleton's head does a 360° vertical flip 

How to reproduce the head flip:

1. Have two skeletons shot each other. 
2. Spawn a third skeleton in between the other two and let him target one of them.
3. Push the third into his target.
4. Now he flips out.