How to populate one dialog list from choices selected in another?

I’d like to populate one dialog list with what’s been choosen in another.

For example field1 contains choices Apple, Pears, Cherries, Grapes. The user selects Apple and Grapes. The choices in Field2 are now Apple and Grapes.

Any ideas?

Subject: How to populate one dialog list from choices selected in another?

Let the contents of the second dialog list be based on a hidden field (computed dialog list and formula point to that hidden field).

This hidden field is filled by some event from the first dialog list.