How does light bend around my finger tip?

When I close one eye and put the tip of my finger near my open eye, it seems as if the light from the background image bends around my finger slightly, warping the image near the edges of my blurry fingertip. What causes this? Is it the heat from my finger that bends the light? Or the minuscule gravity that the mass in my finger exerts? (I don't think so.) Is this some kind of diffraction? To reproduce: put your finger about 5 cm from your open eye, look through the fuzzy edge of your finger and focus on something farther away. Move your finger gradually through your view and you'll see the background image shift as your finger moves. For all the people asking, I made another photo. This time the backdrop is a grid I have on my screen (due to a lack of grid paper). You see the grid deform ever so slightly near the top of my finger. Here's the setup: Note that these distances are arbitrary. It worked just as well with my finger closer to the camera, but this happens to be the situation that I measured. Here are some photos of the side of a 2 mm thick flat opaque plastic object, at different aperture sizes. Especially notice how the grid fails to line up in the bottom two photos.