Independent sitting frees the hands to explore toys in new ways - they typically will pick up a toy, shake it, turn it over, taste it, and pass it from one hand to the other.
A small ball with spikes is an invitation to spend time exploring its properties.
Fundamental hand-object interaction: hold to stabilize, poking with index finger, turning toy for visual inspection, dropping toy,. Social and attention: sharing pleasure
In this video clip you see Lily aged 9 months (CA 8 months) playing with a toy made of a red bell attached to a short ribbon.
She alternates grasping the ribbon and vigorously shaking of the bell with passing the toy from one hand to the other, grasping either the bell or the ribbon.
This video clip nicely shows how infants explore different ways of interacting with a toy. You see Max inspecting the toy, then trying out different movements and rhythms.
In this video clip you see Will playing with two different sized cardboard boxes.
Each box offers different possibilities for action - often referred to as affordances.
Max (11 months) playing with beakers. 
Independent sitting frees the hands to explore toys in new ways - they typically will pick up a toy, shake it, turn it over, taste it, and pass it from one hand to the other. 
As soon as infants can hold an object with a steady grip they start to explore their ability to make repeated reciprocal movements holding the toy.
By the age of 8-9 months TD infants have usually started to pick up, hold and chew or suck on pieces of food such as a wedge of apple. 