apple of discord, the

[тж. the bonе of contention (або discord)]

яблуко розбрату, чвар [етим. міф.];

The apple of discord had, indeed, been dropped into the house of Millbornes (Th. Hardy).

The understandings of this couple were their principal bone of contention, and one great cause of many quarrels, which from time to time arose between them (H. Fielding).

Achilles’ spear

(тж. the spear of Achilles)

щось, що ранить і зцілює [етим. міф.]. 

Achilles’ heel

(тж. the heel of Achilles)

ахіллесова п’ята, уразливе, слабке місце [етим. міф.].