Bubble is a type of Illusion. Bubble is related to Drop. Drop is related to Item. 
Relate is a type of Interact. Relate is a type of Be. Balance is a type of Be. 
Illusion <--IsA-- Bubble <--RelatedTo--> Drop <--RelatedTo--> Item 
Interact <--IsA-- Relate --IsA--> Be <--IsA-- Balance 