The collisions between spheres in the toy with 5 sphere hanging from a string appear to be nearly perfectly elastic so I assume that of two spheres colliding in mid air also is. If so, why is so little kinetic energy lost in the collision. Why doesn't it instead get converted into vibrational kinetic energy? Is it because they collided at low enough speed to have a small contact area in the collision for the reason described in my answer at Why is glass so breakable?? According to my answer at Is the energy conserved in a moving frame of reference?, it's meaningful to define a moving vibrating sphere as possessing translational kinetic energy and vibrational kinetic energy because vibration adds the same amount of total kinetic energy to the sphere as it would if the sphere weren't moving.