rear its ugly head - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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.”