In fact, it's little different to the sound of a crying human baby.

Both big cats and babies make loud vocal noises to attract attention, say scientists.

And both do it the same way, by vibrating similar types of vocal cords.

"Roaring is similar to what a baby sounds like when it cries," said speech expert Dr Ingo Titze, from the University of Utah in the US.

"In some ways, the lion is a large replica of a crying baby, loud and noisy, but at very low pitch."

While babies cried for help, lions and tigers roared to lay claim to their territory.

"In both cases we hear loud, grating sounds that grab people's ears. When a baby cries, the sound isn't pretty. The sound is basically rough. The vibration isn't regular, " said Dr Titze.

The same was true of big cats, which like babies had "very loose and gel-like" vocal cords that vibrate irregularly, he added.

The research, published in the online journal Public Library of Science ONE, showed that lions and tigers roar deeply because of the flat, square shape of their vocal cords.