@Jack: that is really unique and funny! Our cat Oreo says
ooooouuuuuu ooouuuu at the door. The only place she makes this sound. Only thing missing is the "t"

@doydie

It is not just the pee smell....

Cats have scent glands on their feet, and chins. When they rub
their face on objects, they are leaving a "mark" on them. Your late cat has left many "marks" I'd expect. Everyplace your late kitty walked and sat will have her paw scent on it. It is impossible to remove it all. I replaced all bedding of Sheba and Tippy, when they died (it was old anyway). This helped Weezie and Houdini accept our home faster. They don't sit in the same places either.
Washable covers are handy. I have old cotton white diapers, I saved from when our son was an infant, and I use old towels and wash those. This eliminates some of the old scents from our elderly late cats. When Weez was tiny she had a towel she always slept on, on the couch next to me.
Houdini has been very picky about his spots too.

Here is a short article to explain communication:
http://en.wikipedia.org/wiki/Cat_communication

When we go upNorth, our cats check out the house minutely looking for the late great Aunt's Siamese (long gone). Still after 10 yrs!

Watch her eyes. Fear responses, or some types of excitement (like play/stalking),
result in pupil dilation. A cat with constantly dilated pupils is not resting/relaxed unless the room is very dark.
Also cats have complex sensation with whiskers, doing dangling things too close to their face stirs the air which the whiskers register and confuses them.
http://www.petside.com/article/every...t-cat-whiskers
There was a show on cable, I think A &E once that explained how air currents around the whiskers, enable a cat to sense objects in the dark. So this is why cats don't like windy days, and don't respond well to close in the face movement of toys.
When I use the stick with string/feathers, I make it hop up and down and other ways across the room at least 3-4 ft away, so the kitty can sense it better and jump for it. Cats are nearsighted you know, and there are areas they can't see:

http://manhattancats.com/Articles/eyes.html
most people don't know this. 20/200 is rather difficult. For us 20/200 is no driving etc.

If she likes the empty toilet roll cardboard, I bet she would like
the springs. They are only 4 bucks and free shipping for 10 of them. You can also make spirals out of long twist-ems (fold the ends in so no sharp part is exposed), or pipe cleaners (fold the ends in too), the soft cotton ones(not the prickly ones). Our old past cats loved the pipe cleaners, but now with the rolling springs, our young ones disdain the old pipecleaners!

This toy is also fun, and the same principle as the springs. It is available at Petco and other stores locally: These tend to get lost however quickly whereas the springs do not for us for some reason:
http://www.amazon.com/Petmate-Looney.../dp/B00025YVPI

Both of these spring toys seem to move with inertia and mimic the random movements mice make I guess. We have an area in our old house where the floor of the living room is slightly higher than the dining room. It was built that way...Houdini has learned to put a spring on the high spot and watch it roll down and then he catches it. My husband's father used to push toy cars down that same slope...lots of family stories about it. Now Houdini is taking advantage of it! LOL

If she is playing with the empty toilet paper roll, she wants to play.