When did grunts, squawks and other mouth noises become words?
Our protean ancestors possibly understood that mouth noises which sounded like shrieks and screams meant danger. Presumably, they began to discern what kind of danger lay ahead by the pitch and intonation of the scream.
But surely they learned sex and fear simultaneously in their evolution, so moans and screams sounded alike. Thus they had to invent context. If there were moans before screams, things were OK. If there were no moans before screams, things weren't OK. In that case, screams could have meant "wrong hole" before they meant "danger."