Expression is related to Glad. Glad is the opposite of Sad. 
Comfortable is derived from Comfort. Comfort is related to Clothes. Clothes is related to Closet. you are likely to find Dust in/at/on Closet. 
Expression <--RelatedTo--> Glad <--Antonym--> Sad 
Comfortable --DerivedFrom--> Comfort <--RelatedTo--> Clothes <--RelatedTo--> Closet <--AtLocation-- Dust 