Trunk is related to Limb. Limb is related to Walking. Walking is related to Slow. Slow is a synonym of Boring. 
Unhappy is a synonym of Low. Low is a synonym of Flat. 
Trunk <--RelatedTo--> Limb <--RelatedTo--> Walking <--RelatedTo--> Slow <--Synonym--> Boring 
Unhappy <--Synonym--> Low <--Synonym--> Flat 