Reminds me of the time I had seen my dog sneaking down the hallway a few years back. Some how she knows when she shouldn't be doing something, she just gets that look. But at the time I had a FW tank with a few crabs in it. One had managed to get out and was crawling around. She had picked it up every so gently in her mouth and was taking it to a secluded spot to presumably have a little snack. Luckily I had seen the sneaking and rescued the crab.
Then again it may be my fault. Knowing that dogs are creatures of habit, she may have gotten used to the treats I would give her. I used to work at Red Lobster and they throw out their old product after 48 hours of receiving it. Well lets just say the dog ate very well. Lobster, fish and her favorite shrimp. Funny thing is she couldn't eat anything cooked, it had to be raw. She tried like crazy to eat the it cooked but it was just too much like rubber for her. She'd end up spitting it out leaving a soggy surprise for me to find later.