We see, among other things, the effect of refraction through the glass. The checked pattern on the wallpaper is critical in this respect. We compare the pattern as seen directly with the pattern as seen through the glass, and the distortion is immediately interpreted as the effect of refraction through a curved, transparent surface. Notice also the difference between the effect as viewed through both sides of the beaker and the effect, at the top, where we see only through the back side of the beaker. This usage may seem a little crass when speaking of what is undoubtedly art, but the 3-D artist is always thinking about what it takes to convince the viewer of the reality of a rendered scene.
Little things make all the difference.
Standing 15 feet away from a portrait in a museum, we see a touch of warm sunlight caress the subject's nose. The skilled painter understands those cues that the viewer will instantly interpret as reality. The 3-D artist must learn the same. In the case of the glass beaker, the refraction sells the object, and where the refraction is less obvious due to the background, the effect is weakened. Compare the identical scene with the checkerboard pattern removed from the surface of the wall.