I remember hearing a comedian say that in the famous Last Supper painting, there is very little food on the table, just fish. He said that it must have been painted on a Friday because if DaVinci, being a Catholic, had to forgo meat on Fridays, the Jews weren't going to have it either.
As far as there being a guinea pig in the Peruvian painting, that would only be natural. I haven't been to Peru but I have been to Ecuador and guinea pig is a very common dish. They grill them out on the sidewalk and sell them to passers-by. They still have their teeth and tails. I've eaten a lot of strange things (I ate roasted grubs in Ecuador) but I had to draw the line at guinea pig. I had numerous guinea pigs as pets in my youth and I could not stomach eating one of my pets. I'm sure it's quite tasty but it would be like eating dog or cat.....