1
general::
Phrase(s): rear its ugly head
Fig. [for something unpleasant] to appear or become obvious after lying hidden. • Jealousy reared its ugly head and destroyed their marriage. • The question of money always rears its ugly head in matters of business.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Appear. This phrase is used only of something undesirable or unpleasant, as in The interview went very well until a question about his academic record reared its ugly head. This expression was first recorded in slightly different form in Anthony Trollope's Barchester Towers (1857): "Rebellion had already reared her hideous head."
American Heritage Idioms