In the poem 'Then and now' written by Oodgeroo in her book of poems 'My people', what sudden change takes place in the tone for the rest of the first stanza ,written below:

In my dreams I hear my tribe
Laughing as they hunt and swim,
But dreams are shattered by rushing car,
By grinding tram and hissing train,
And I see no more my tribe of old
As I walk alone in the teeming town.
I have seen corroboree
Where that factory belches smoke;
Here where they have memorial park
One time lubras dug for yams;
One time our dark children played
There where the railway yards are now,
And where I remember the didgeridoo
Calling to us to dance and play,
Offices now, neon lights now,
Bank and shop and advertisement now,

The sudden change in tone occurs when the speaker mentions the "rushing car, grinding tram, and hissing train." The tone shifts from nostalgic and reminiscent to one of sadness, lamenting the loss of their traditional way of life and the encroachment of modernization. The tone becomes more critical and regretful as the speaker describes the transformation of their tribal land into a bustling and urbanized town, where factories belch smoke and commercial establishments take the place of their ancestral grounds. The speaker's tone reflects a sense of longing and mourning for the loss of their tribe's culture and connection to the land.

In one sentence

The sudden change in tone occurs when the speaker laments the intrusion of modernization, such as cars, trams, trains, factories, and commercial establishments, which replaces the traditional way of life and evokes a tone of sadness and regret.