To make a valid post in this game, you may:
1) Post an interesting fact related to the number of bells/weed you claim (according to Tumbleweed rules).
2) Alternatively, you may post an interesting fact about bells or tumbleweeds.
3) Alternatively, you may claim a number of bells or weed exactly one more than the number claimed in the last claim, be it bells or weed.
4) You may as an alternative move post a picture of a bell or a picture of a tumbleweed or a picture related to one of the interesting facts mentioned before.
Examples
1) 18 bells - 18 is the legal age for drinking in the UK
2) The tumbleweed is found in the desert
3) 19 bells (if the last claim was 18)
Other rules:
5) If an invalid claim is made, the clock is reset to zero and the number of bells and/or weed claimed resets to zero.
6) Consecutive posts are banned when posting according to rules 1 and 3, but you may post consecutively according to 2 and 4.
The earliest evidence of the use of bells comes from the 3rd millenium BC, in Ancient China.