What happens when multiple funnels share the same trigger?

When multiple funnels share the same product of collection trigger you can determine which funnel to display by using the Manage priority functionality of the Funnels page. 

For example, if Funnel A and Funnel B are both set to display if your customer purchases a particular product, you can choose which has the higher priority by dragging the funnel you want to display first to the top.