“Af hverju?” means “why?”.[a] It has an extremely slurred pronounciation and is in most cases pronounced [a(h)kkuru].
“Af því að” means “because”.[b] The letter V in “því” is usually not pronounced,[c] and even the F and the Ð are quite soft in this phrase so they also disappear.[d] The pronunciation is therefor [a þí a].