I tried to play a trick/joke on DD this a.m.  I crawled into a small tent in her room, which has a front and back flap.   I entered on the far side from her door when I heard her coming up the stairs.  She came in her room and, not noticing me, picked up some dolls and started playing with them and "talking" for the dolls.

After a minute, I took one of her stuffed cats (which were already in the tent), and slowly pushed him out of the flap on DD's side of the tent.  Suddenly, she stopped talking and playing, and froze in place, staring at the cat.  I'm not sure if she saw it move, but she noticed that it hadn't been there when she sat down.  She stared with a quizzical look for 20 seconds or so, then smiled, walked over to the tent, and opened the flap laughing at her Mommy's trick.

Then again, she's used to her "tricky Mommy."  She enjoys scaring us and us scaring her back.