One interesting thing about the Hebrew alphabet (known as the alephbet for its first two letters, the aleph and the bet) is that it contains two characters with no sound. They are silent when alone and may serve as a pause, a spacer. More commonly they are used in conjunction with vowels, giving the vowel sound without a consonant sound modifying it. The two characters are the Aleph, and the Ayin. Either of those two characters can be modified as follows:

Line under-- Sounds like "ah"
"T" under-- Sounds like "ah" or "aw"
1 dot under-- Sounds like "i" in "machine"
2 dots under (horizontal)-- Sounds like "ay"
3 dots under-- Sounds like "eh"
2 dots under (vertical)-- silent if at end of a syllable

Also, the character "Vav" can have vowel sound:

1 dot above-- "o" sound
1 dot in middle-- "oo" sound

Of course, this may all differ a bit depending on Sephardic or Ashkenazic choice of pronunciation.

Edit: Gartogg says "The ayin does have a gutteral sound, like the sound of swallowing, and different israelis either pronounce it, or do not. The grammatical rules reflect it's gutteral nature."