Why do you think that the ancient Egypitians used these particular pictures to symbolize sound?

Answer 1

It is theorized, by Anthropologists and Linguists, that early man would give a common name to an animal or an article; something recognizable when you think of it. The Egyptian word for cat, as an example, was "Mau" basically reproducing the "meow" of a cat; taken from demotic script.

What it boils down to is: the pictures used by Ancient Egyptians, in Heiroglyphs, were originally meant to represent ideas or concepts. They evolved to consist of three kinds of glyphs: phonetic glyphs, including single-consonant characters that function like an alphabet; logographs, representing morphemes; and determinatives, which narrow down the meaning of logographic or phonetic words