Xray

Use the Xray filter to make something look like an x-ray.

For example:

If you want to see a working example, you can look at the Filter Effects page. This HTML page shows the effects of all the visual filters. For each filter, there is an example. Underneath the example, there is a box for each parameter. You can change the values for the parameter and click on the Change button to see the effect. The Reset button restores the example to the initial state.