cuernos
B2 · adv
the hell, on earth (for emphasis after a question word)
cuernos = horns; 'what the horns?' is a mild oath, like 'what the heck?'
Spanish ¿qué cuernos...? uses cuernos (horns) as a softened swear after a question word, much like English 'what the heck'. Link: horns plus devil, so a mild stand-in for a stronger curse.