I don't know if this happens to the rest of you cat owners out there, but my cat Tigger seems to have a sixth sense when it comes to my changing the bedsheets. As soon as I so much as take off one corner of the bedsheets, he appears in the doorway with an inquisitive look in his eye. If I stop what I'm doing and just stare back at him, he will usually walk away. But if I continue removing the bedsheets, then he leaps forth and pounces on my bed, seeing this an initiation for play time.
This is Tigger posing mid-play from earlier today. I got two scratches on my right hand for my troubles, but I don't mind. Play time with Tigger happens to be fun for both of us. (: