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The character on the right has a lot of jerky/snappy-ness happening. It gives me the impression that maybe it has excessive or redundant keyframes that don't support the intended motion, and also that maybe some IK targets moved of range of their bones. Keep a close eye on your keyframes to catch strays, and sometimes just blanket-delete an entire section and redo it if the motion has become too complex for your rig or platform to support. About the stiff arms, try to make sure your IK targets only even reach their maximum length when you need to indicate tension (like stretching/pulling). Outside of those situations, things like arms will always feel a little more natural if their IK targets stay close enough to allow for a slightly relaxed angle.
I love the expression on the left character. Good subtext happening there.
These Character need to settle down in a pose. Bad hand animation and your hiding the lip sync.
Your primary character has a bad case of jiggly arms. You are letting the computer take control of your animation. And your secondary character finger goes through each other (Frame 67+).
Animator: Diego Vazquez
Description: Hi, this was a homework for my university, thanks for stopping by.
Experience: 1 semester
Time taken: 4 days