Disclaimer: sorry, major derailment up ahead.
The Goya reference made me think of this picture
.
Resistance is obviously very strong in Mexico (for a start, it's the only developing country that shares a border with the US!) especially in areas where there is still a sizeable indigenous population and the ancient knowledge is still part of everyday culture. I've been thinking a bit about corn as a symbol of resistance today, thanks to your mention of it, Gavin, and I've noticed how things like the GMO corn issue strike a much deeper chord here than elsewhere, possibly because it's seen as the ultimate destruction of Mexico's indigenous heritage, which goes way beyond the anti-corporate, environmental or human health angle you get elsewhere (this is a topic in the Future of Food documentary, too, which I really recommend if you haven't already seen it).
Crop circle in a field of GMO corn. This is in the state of Mexico in the central part of the country.
Millions of Mexicans are dependent on rain-fed corn grown as a subsistence crop, in southern Mexico alone over 200 types of corn are grown and there is a huge stock of knowledge about traditional agriculture. This wealth is in serious danger of disappearing with the continued influx of GMO crops and the extension of industrial plantations. People on the land are very aware of this and try to resist it at every level - it is no coincidence Oaxaca and Chiapas are hotbeds for civil unrest and are under de facto military occupation. For example, there was an enormous uproar in Oaxaca (led in part by artist/activist Francisco Toledo) when it was announced a McDonald's* was going to open on the zócalo (main square) of Oaxaca city - fast food triumphing in the heartland of Mexican food culture - the symbolism of this struggle is staggering because you are not only protesting against the animal rights, worker issues, health effects and environmental damage, but the undermining of people's identity and their creation myth. Thus the ears of corn on the murals are not only a reference to the artist's homeland but a shorthand form of expressing a long and complex relationship about identity (you will often hear people in Mexico emphatically stating they are "men [made] of maize", which I think is a nice contrast to the traditional "dust").
(* McD's finally did open a very low-key franchise near the university. Last I heard, it was firebombed by protesters last December)