I sat on the ball and rolled into position, ready to do a sit-up. I sat up, I relaxed back down, and a dog materialized in my lap. She then crawled up and laid down on my chest. Apparently, she doesn't think I need to exercise today.
After a few minutes, she got up, and I tried another. She materialized again.
So I'm giving up for now. I'll see if she supports my attempts at fitness later this evening. And if she doesn't, she may go sleep in the kitchen for a while, because I'm very close to fitting into my summer shorts. Don't say anything about how far into summer we are.