My kids love cool (/ gross!) sensory activities, and so I'm always on the lookout for fun things to explore together. We've explored oobleck here before, and when I saw this project for homemade slime on this awesome site, I knew we had to check it out during the Halloween season.
Borax (sodium tetraborate) is a naturally-occurring mineral salt commonly used as a laundry booster or cleaner. As with any other cleaning product, it should be kept away from children not under direct supervision of an adult. Do not allow children to ingest Borax. If consumed, contact a poison control center immediately. Wash hands after play, as prolonged skin exposure may cause irritation.