On the left is a picture of a big bottle. We can absolutely imagine popping the top and drinking the beer in the bottle, but very few would wash the bottle out and use it as a glass. But what if the top of the bottle didn't exist, as in the picture on the right? In that case, once we would have had a beer from the "bottle," we would probably think that we could reuse it, and then keep it as a glass, just like many people do with Ball jars. But again, we can easily use the bottle to fill water from a tap, and just use it as a glass. (You may know that in many countries, the tops of bottles are cut off; the bottoms then serve as glasses.)
Therefore, it seems that the difference is the social learning that one shape is acceptable to use only in certain ways, when in fact, there is very little difference between many of the objects we think are different. This raises several interesting questions about design and learning and behaviour. There are probably very small things we can do physically to common objects such that we might think they are multi-purpose. These changes can have huge consequences - reduced quantities of things going to landfills, reduced need for recycling, increased reusing, increased sentimentality, increased pass-me-downs, decreased natural resource extraction, etc. etc. etc.
The other night, Marco raised the very interesting case of the bee in the urinals (here, here). Here's a picture of the bee.
What this simple little change has done (you can read why by clicking the above links), particularly in high-volume places such as airports and malls, has been to reduce the amount of cleaning required, the chemicals required for cleaning, the water used for cleaning, and on and on. Maybe it is worthwhile to think about how we can make just small changes to what surrounds us to change our perceptions of use. It would be interesting to see how the learning is passed between people with these changes.