the mischief is done); to look a gift horse in the mouth (= to examine a present too critically; to find fault with something one gained without effort); to ride the high horse (~ to behave in a superior, haughty, overbearing way. The image is that of a person mounted on a horse so high that he looks down on others); the last drop/straw (the final culminating circumstance that makes a situation unendurable); a big bug/pot, sl. (a person of importance); a fish out of water (a person situated uncomfortably outside his usual or proper environment).
Phraseological fusions are word-groups with a completely changed meaning but, in contrast to the unities, they are demotivated, that is, their meaning cannot be deduced from the meanings of the constituent parts; the metaphor, on which the shift of meaning was based, has lost its clarity and is obscure.
E. g. to come a cropper (to come to disaster); neck and crop (entirely, altogether, thoroughly, as in: He was thrown out neck and crop. She severed all relations with them neck and crop.); at sixes and sevens (in confusion or in disagreement); to set one's cap at smb. (to try and attract a man; spoken about girls and women. The image, which is now obscure, may have been either that of a child trying to catch a butterfly with his cap or of a girl putting on a pretty cap so as to attract a certain person. In Vanity Fair: "Be careful, Joe, that girl is setting her cap at you."); to leave smb. in the lurch (to abandon a friend when he is in trouble); to show the white feather (to betray one's cowardice. The allusion was originally to cock fighting. A white feather in a cock's plumage denoted a bad fighter); to dance attendance on smb. (to try and please or attract smb.; to show exaggerated attention to smb.).
It is obvious that this classification system does not take into account the structural characteristics of phraseological units. On the other hand, the border-line