They speak, but they don't speak "as such".
Hold on! my dear friends
They have no dearth of desire to express - expressions,
They are not deaf either - my Friends.
They open their their mouths, lips do move,
Alas! The energy that comes out moves just the gas, fail to produce sound waves,
Or my dear friends,
They energy does produce sound waves,
Might be the frequency is not audible to us!
They say, reasoning has no significance,
If it fails to provide positive explanation.
But there can be another explanation, less interesting with even lesser acceptability.
Probably they produce sound waves, probably even frequency is audible,
Probably they simply don't speak, what they call "positive".