The only excerpt here that includes both alliteration and onomatopoeia would be: They did not know it was Mr. Sniggers putting paris green on the potato plants. A big drop of paris green spattered down and fell onto the heads and shoulders of all three, Eeta Peeca Pie, Meeny Miney, and Miney Mo.
Alliteration is the repetition of the same consonant as in - Peeca Pie, Meeny Miney, Miney Mo.
Onomatopoeia is mimicking the sounds heard in the nature. The only such word here could be - spattered, although even that is far-fetched.