Why is it ironic when Zizag says, "Two rattlesnakes. Two scorpions. Two yellow-spotted lizards"?

In Holes, Zigzag makes this comment when a big storm seems imminent in the desert. He, Stanley, and several other boys are out in the desert when they hear thunder and see lightning. The dark shape of the mountains is also illuminated by the lightning flashes. Squid speculates that the hard rain might fill up the lake so they can swim. X-Ray jokes that they should make an ark (like Noah) to hold them for 40 days and 40 nights.
At this point, Zigzag suggests sarcastically that they load up pairs of the desert animals, two of each. The three types of animal he names are all potentially lethal if they bite or sting a person, but an ark would have to save every type of animal.
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