Ouch! Ah! Eina! This is what an Englishman, a Swede and a South African would exclaim respectively if they experienced intense emotion or a sudden painful sensation . They correspond, in any case, to the Castilian "ay!" And, although the tongue varies, the mechanism is essentially the same: practically involuntarily a loud sound is emitted with the mouth open . It is, in fact, the fastest way to do it.
This has led some experts in etymology to suspect that, originally, this expression must have been used as if it were an alert mechanism to warn other congeners of the presence of a danger.
