Mental is similar to Psychological. Psychological is related to Mind. Mind is a synonym of Heart. 
Kill is related to War. War is related to Elephant. Elephant is related to Gray. 
Mental <--SimilarTo--> Psychological <--RelatedTo--> Mind <--Synonym--> Heart 
Kill <--RelatedTo--> War <--RelatedTo--> Elephant <--RelatedTo--> Gray 