what does it mean?

[Ksunya]

Hello, again
What does this sentence mean?

Sensing the treacherousness of the ground they were treading, he checked himself in embarrassment.

Thanks in advance

[Tdol]

What's the wider context? It could either mean that the physical ground is unstable or, more probably, that they are touching on sensitive issues, so he stopped in embarassment.

[Ksunya]

The thing is that I don't have wider context. There are only separate sentences given in the book, so I have to translate it, but confront with a lot of difficulties.
I have one more sentence :

Even Mr. Jaggars started when I said those words. It was the slightest start that could escape a man, the most carefully repressed and the soonest checked, but he did start.

What did he start? I read it millions of times, but can't get it maybe, he jumped?

[Anglika]

The thing is that I don't have wider context. There are only separate sentences given in the book, so I have to translate it, but confront with a lot of difficulties.
I have one more sentence :

Even Mr. Jaggars started when I said those words. It was the slightest start that could escape a man, the most carefully repressed and the soonest checked, but he did start.

What did he start? I read it millions of times, but can't get it maybe, he jumped?

In this context the meaning of "start" is : a sudden involuntary movement, so yes, in a sense he "jumped".