If someone says, you need to work on your physicality, what are they really saying? This is such a large topic. Making something seem physical can be related to weight or how the character holds themselves. It can be how a gesture feels wooden and non-physical. Lets talk a bit about the latter. When a character makes a hand gesture, it not only needs to communicate what the character is doing, but needs to feel as if the character has flesh and bones underneath. You need to understand the anatomy of the character you are animating. One of the biggest things that makes computer animation not look so good is that people do not pay attention to this. The computer will and can ruin good poses if you do not do the in-betweens and breakdowns correctly. It has no knowledge of all those things you should be putting in there likes arcs, overlap, slow ins, cushions, overshoots, anticipations, squash and stretch, straights and curves, contrast, etc, etc, etc.
If you want a sample case, I was working on the teaser for Monsters Inc. Mike does a gesture and then drops his arm. I really wanted to understand how that works so I did a bit of reference and it helped me understand the weight the arms has and how it comes to rest. A lot of what I am talking about has to do with this. Residual energy. I’ll get into this more at a later time, but residual energy really has a lot to do with how your character recovers form hitting a pose or gesture. In essence it is overlap and follow through. One thing you do not want, is for the character to become over animated, so you really need to understand how to use it and where it is called for.
I hope to put together a better set of examples and post them at a later date.