Nima will catch cross-contamination/cross-contact instances where foods may be cooked in the same oil (chips, for example) or in the same water (such as gluten-free pasta being cooked in the same water as wheat-based pasta).
Nima can only test the sample of food placed into a capsule. There may be times when cross-contamination occurs in food handling that Nima will not catch if you sample from a different area on the plate. There are tips and tricks to help Nima account for certain methods of cross-contamination, but even with the extra data Nima can provide, you should always use your best judgment in choosing what to eat and what to avoid. Always have a thorough discussion with your server regarding food allergies or sensitivities.