Ah, easy.
Do you know the comic "Hägar the Viking"?
In one strip Hägar's wive Helga tells their son Hamlet to never lie, as that causes the horns to fall off a vikings helmet (yes, they got horned helmets in that comic).
Hägar passes by and Helga asks him a question, which he answers, causing -one- of the horns from his helmet to fall off.
After that, she turns to Hamlet and says:
" See? A half truth."