bicubic interpolation of jello nodes
catmullpatch.java Cubic.java

To control the 16 constraints, use the keys in the block below. Press shift and the key to move the constraint up instead of down.

1234
qwer
asdf
zxcv
If you press the bracket keys
[]

it will change the tension in the splines. (This just affects some of the coefficients in the matrix we multiply by.)
The bouncing effect is hand-tuned so it isn't really precise. You have to wait for it to stop bouncing before you press the same key again.

Spline applet
catmuller.java Cubic.java
This is a simple row of Catmull-Rom splines that you can drag around and play with. A hint for interacting with the applet: Click on the node you want to move, let up the mouse button, and then press it down again and drag it.