Crocodile bulks of swallowed prey flesh and bone. Many large crocodilians swallow stones (called gastroliths or stomach stones), which may act as ballast to balance their bodies or assist in crushing food, similar to grit ingested by birds. Herodotus claimed that Nile crocodiles had a symbiotic relationship with certain birds, such as the Egyptian plover, which enter the crocodile's mouth and pick leeches feeding on the crocodile's blood; with no evidence of this interaction actually occurring in any crocodile species, it is most likely mythical or allegorical fiction. Since they feed by grabbing and holding onto their prey, they have evolved
Symbiotic bacteria are endosymbiont. Certain plants establish a symbiotic relationship with bacteria, enabling them to produce nodules that facilitate the conversion of atmospheric nitrogen to ammonia. In this connection, cytokinins have been found to play a role in the development of root fixing nodules. It appears that not only must the plant have a need for nitrogen fixing bacteria, but they must also be able to synthesize cytokinins which promote the production of root nodules, required for nitrogen fixation. Symbiotic bacteria are able to live in or on plant or animal tissue. In digestive systems, symbiotic bacteria help break down foods that