What Am I Riddles

Question: In a marble hall as white as milk, Lined with skin as soft as silk, Within a fountain crystal clear, A golden orb does appear, There are no doors to this stronghold, Yet thieves break in and steal the gold. What am I?

Question: Travel a mile and I will change.
Travel a million and I will end as I started.

What am I?

Question: I am almost nonexistent through sorrow, yet am frequent through happiness. I have no contact, yet I am contagious. What am I?

Question: You put me on a table and cut me, but you don't eat me.

What am I?

Question: I run over fields and woods all day. Under the bed at night I sit not alone. My tongue hangs out, up and to the rear, awaiting to be filled in the morning.

What am I?