I have a dog who is a little too smart for his own good (or mine). I've written before here and then again here about how he works out sneaky ways to get toys and bones away from his sister. Now he's trying to pull a fast one on us. One of his bad habits is eating tissues. He'll get them any way he can. He's smart enough to know he isn't allowed to do this, so like any addict, he's modified his tactics in order to get his fix. When he finds a tissue he either tries to grab two or he tears the one he does find in half. Then he keeps one tissue in his mouth hidden, and allows the other one to be visible.
On two separate occasions, we have caught him with a tissue and told him to spit it out ("leave it!" is our command for this) which he dutifully does. After I disposed of the first tissue, I noticed he had a second one he was just finishing up. He pulled the same con on Shauna today. I don't know whether to be annoyed or proud. :-)