I've drawn a slime monster in Inkscape (so I can resize to any resolution required).  I'm trying to make it look like a monster made out of a very stiff gelatin.  To that end, I'm working on an animation to play whenever it's disturbed by a collision.

Here's an animated gif I captured of the jiggle animation, as taken from my game engine:

Here's the current version of the sprite sheet:

As you can see, when struck, the slime jiggles.  Something about this animation is bothering me, every time I see it running, but it's probably just me being a perfectionist.

What do you think?  Can you see any way I could improve this little sequence?  Thank you.

After talking with a friend about it, it became clear that what was bothering me was a lack squishing on the part of the slime and it needed to jiggle just a little, even in it's rest state.

Here's the new gif (I decided to put it on a checkered background this time):

Here's the new sprite sheet:

In the first version the slime definitely needed some more motion! The squish you added to it really helps!
I think that it could look more interesting if you exaggerated the squish a bit more, but you also mentioned that its a very stiff gelatin, so it could work as it is too!  

I finally got my slime fully working the way I wanted, both on the art side and the code side.  It jiggles when hit, stares at enemies in an aggressive way and jumps at them.

Here's a Slime I tricked into doing a circus act (the ball is a decoy prop that triggers it's attack behavior, without which it just sits there):

Here's the newest sprite sheet:

The slime is now published as  part of my game engine.  If you're interested in that, it's called Big Block Engine.  If you want to use this sprite, it's license is CC-BY-SA 3.0.  For the attribution part, I'm Richard Lewis and if possible please share a link to my game engine when you credit me.