The effectiveness of any rat bait depends upon environment and the habits of the rat in question. Rats tend to avoid new objects, so traps take some time to be effective. Traps can be made more effective if an attractant, sometimes called a bait, is used. Because rats are scavengers, the most effective rat attractant is food. Fruits and vegetables are attractive to roof rats. Meats or fish are more attractive to Norway rats. However, it is best to utilize food baits that are not likely to spoil in unreachable locations. Peanut butter should not be used since some people are allergic to the smell of peanuts. Another possible attractant would be nest materials such as bits of string, yarn or even cotton balls.