Strange vote buying

Eric Crampton at Offsetting Behaviour reports on vote buying in Tanzania. It looks likely that both the government and the opposition bought voter cards in areas where they were likely to face greater opposition. Nothing strange in this in many parts of the world. But what is strange is the going currency: Mattresses!

Mattresses? Why Mattresses? These are not the most obvious choice for a medium of exchange for any transaction. To be widely marketable, a medium of exchange should possess the following characteristics:

1. transportability
2. divisibility
3. high market value in relation to volume and weight
4. recognizability
5. resistance to counterfeiting

Apart from, may be, item 4 I don't see mattresses as have any of these characteristics. So how is it that you can buy votes for them? There are some very strange markets out there!

What would Menger's theory of money look like if the medium of exchange was mattresses?!