Lay or Lie? -- or Just Losing my Mind!?

This has been driving me nuts for years.  Before reading any further, ask yourself, "Do I really know the difference between the words lay and lie?"  If you're like me, laying/lying (?) in bed, having trouble sleeping at night, not knowing if you are using the words properly, prepare to get a good night's rest.  Here's the story that I learned after doing a little research.

"Lay" is a transitive verb.  That means it must have some sort of action and is always followed by an object which receives the action.  "Lay" means to place something.  I lay my bag on the table.  (The action is me placing, and the object is my bag.)  If you did it yesterday, you laid your bag on the table.  You may also have laid many bags on many tables.

"Lie" is intransitive and means to recline.  It doesn't need an object to receive the action.  The boy lies down.  (The boy is the subject, and he's reclining, but there's no object receiving anything.)  Here's where it get confusing: the past tense of lie is lay.  So, the boy lay down yesterday.  He has lain down each day this week.

Try to fill in the blanks with either: lay, laid, lie, lay or lain.
1.  I was exhausted last night, so I ______ down for a quick nap.
2.  She ______ the baby in the crib each evening.
3.  Every morning this week, the dog has _____ on the concrete floor to cool off.
4.  My mom _______ the cards on the table.
5.  The cat _______ still waiting for the mouse to move.


ANSWERS:
1.  lay
2.  lay(s)
3.  lain
4.  laid
5.  lie(s)

How'd you do?