Funneling takes the selected choices from an item on a previous page and "funnels" them into a future item. Only the choices that the user selected in the first item will be shown as options for the future item. This allows for more relevant follow-up questions to gain additional information from users.
You can funnel choices from a source item to a destination item. These two items need to be separated by a Page Break item. Add the choices to the source item. Edit the destination item, using the "Funnel Choices" input method. While in the Form Editor or when viewing/editing results, all of the possible choices will appear in the item. When a user is filling out the form, only the selected choices from the source item will be presented as possible choices in the destination item.