Mental is related to Memory. Memory is related to Stuff. Pad is a type of Stuff. 
Portion is related to Bit. Bit is related to Bullet. Bullet can be used for Killing. 
Mental <--RelatedTo--> Memory <--RelatedTo--> Stuff <--IsA-- Pad 
Portion <--RelatedTo--> Bit <--RelatedTo--> Bullet --UsedFor--> Killing 