Section 2 of Holes has a theme of never giving up!!!
In this section their trying to get to God's Thumb. Although their tongues are dry, their feet are sore, their sweating like crazy, and one of them is having sharp stomach pains, you can infer that they are persevering through all of this to get to the top of God's Thumb.
As they are climbing up God's Thumb, he is struggling to carry Zero while he is unconscious from dehydration, and starvation. Although this is going on, he still is determined to get to the top of this rough mountain.
Let's go back to the beginning of section 2. Stanley has just runaway from camp and is now searching for God's Thumb and maybe even Zero. Although he us still not finding either of them he is still pushing through so he can find Zero, and even find Gods Thumb.
At this point, they are in the hole they dug to hopefully find buried treasure. The good thing is, they found a chest! Bad news... Mr Sir, Mr Pendanski, & the Warden had caught them in doing so. They sit still as there is a nest of yellow-spotted lizards surrounding them. Even though they are highly afraid of these fierce creatures, they push through this fear and keep their cool for about 7 hours!!!
Once again, let's go back a little earlier, when Zero runs away from camp. You can infer from Zero's point of view that he did not give up, as he was found under an old boat, trying to survive.
When they were almost to the big thumb, Stanley is scared that he and Zero might not find refuge on big thumb at all. Yet again, we can see that he is persevering through his fear of this because he knows its their only hope.