What are some common Hink-Pinks?

Hink-pinks are riddles that focus on the pronunciation and meaning of words to trick the solver. Here are some examples:

> What has keys, but can't open locks? (A piano)

> Forward, I'm heavy, but backward, I'm not. What am I? (The word "not")

> What goes up and down but never moves? (A staircase)

> What is always in front of you but you can't see it? (Your future)

> What has a bed but no head or feet? (A river)

> What has a neck but no head and wears a cap? (A bottle)

> What is black when you buy it, red when you use it, and grey when you throw it away? (Coal)

> What is so fragile that saying its name breaks it? (Silence)

> You measure my life in hours. I serve you by expiring. I'm quick when I'm thin, and slow when I'm fat. The wind is my enemy. (A candle)