Many dogs become scared of unfamiliar objects, like bicycles or vacuums, the older they get. If you have a dog that's never seen a skateboard, they might freak out on a walk if someone skates near them suddenly one day. Exposure to bicycles, skateboards, household appliances, and sports equipment early on will help prepare them for unexpected encounters in the real world. You should introduce your puppy to a variety of objects during their first months. You can start by leaving the objects out near them so they can sniff and explore them. If it's an object you use (like a vacuum cleaner), work up to using it around them. If they appear scared, give them some treats or let them back off until they feel safer (especially if they don't eat the treat). You can keep doing this with less frequency the older they get to keep them used to seeing new things.