One of my old posts, from way back in 2006, which remains popular is: Roman builder ... whoops (yup, Roman builders did mess up and try on just as many excuses as modern ones).
And, rather in the vein of surgeons forgetting to remove an implement today, it seems that mummifiers could also mess up ... although since the person being mummified was already dead, I guess that was less of an issue.
This is the second ever example found in a mummy of the tool mummifiers used to remove the brain.
Oops! Brain-Removal Tool Left in Mummy's Skull - Live Science