When infected with the bacteria, initial symptoms include drooping eyelids, blurred or double vision, dilated pupils, difficulty speaking, trouble swallowing, dry mouth, and constipation. One tip for preventing infant botulism is to avoid giving honey to babies until 12 months of age. Foodborne transmission occurs through the consumption of poorly preserved foods, especially homemade vegetable preserves in oil. Signs of contamination include swelling of the jar or lid, often accompanied by a "clicking" sound when opened. In these cases, the food should be discarded immediately.