Dave's investigations know no bounds. He has been known to tip over the trash can to sift through the contents in search of something good to eat. It's not that he doesn't already have enough food provided for him, it's just that he can never be 100% certain that there will be more food tomorrow. There is no amount of assurances that would suffice. That's what happens to you when you grow up on the mean streets of Iowa. You have to fend for yourself, and if that means tipping over a trash can, so be it. You wouldn't judge if you knew what Dave has been through.
He has knocked over the trash can so many times that it now has to be weighted down with a brick to make the tipping-over harder to do. Dave still tips it over if he really wants to, but not as much as he used to.