there are four ways to do this.

method 1 plastic bottle cap ninja dart: 1. remove the lid and plastic ring from the plastic bottle. The bottle cap can be used as the basis of darts, and the plastic ring originally set on the bottle can be used as the base point of darts. Choose plastic bottles with caps and plastic rings connected together. Sports drink bottles are the best, because they have the largest openings, so the caps are the largest. Use a water bottle, a tea bottle or a soda bottle. 2. Turn the plastic ring out. Turn the plastic ring out with your fingers so that its "thorns" or sharp handles face outward. Press the inside of one side of the ring with your thumb. 3. Slide the lid into the ring. Move the plastic ring outside the cover until it is completely covered. Put the ring on the cover, and the opening of the ring should be aligned with the top of the cover as accurately as possible. 4. Adjust the ring thorn as needed. All the thorns on the ring should stand up. Carefully turn your thumb against the direction of the stab. This should make the thorns stand on end. 5. Admire your work. Your ninja darts are now complete. Don't throw this dart at people or animals. This is not a particularly dangerous dart, but it will still cause harm if thrown at people or animals.

method 2: 1, cut off the handles of four plastic knives. Cut off the handles of four picnic plastic knives with scissors or sharp knives. Leave a handle about 1 inch (2.5 cm) for the blade. This short hilt is reserved for overlapping blades later. 2. Glue the two blades together. Glue the two blades together and overlap them with the remaining handle. Tie them with scotch tape. Note that the directions of the two blades should be opposite to each other. One blade faces to the left and the other to the right. 3. Glue the other two blades together. Glue the other two blades together like the previous two. Overlap at the residual hilt. 4. Connect the two sets of blades together. Overlap the center of one set with the center of the other set. Glue the two sets together with transparent glue. Note that the four blades should face the same direction during operation. 5. If you want, you can trim the edges. Trim the head of each blade into a 1-inch (2.5 cm) tip with sharp scissors or knives. It is not necessary to do this, but adding a tip can make darts stick to cardboard and foam targets better. 6. Check your finished product. Play with the flat surface of each blade with your thumb and forefinger. Add adhesive tape as needed to keep the blade from loosening. At this point, the dart is finished. Only throw darts at inanimate targets such as cardboard and foam, and never throw them at people or animals.

Method 3: 1. Put the blades of two art knives together. Line up the two blades so that the tails are edge to edge. Note that the blades of both knives should be outward. The functional blade you want to use must be a "pen" type functional knife. 2, careful use of double-sided tape. Put a piece of double-sided adhesive tape on the base of the two blades for temporary fixation. If there is no double-sided adhesive, you can fold the single-sided adhesive instead. Fold the non-stick side of the single-sided adhesive until the two ends overlap. Overlap enough tape so that the adhesive surface at one end extends to the non-adhesive end to form a circle. 3. Put the other two blades on the tape. Put the bases of the other two blades on the tape. Press gently to fix. Note that all sharp edges of blades should face outwards, and the four blades should face in the same direction during operation. 4. Secure the darts with more tape. Wrap the general tape around the center of the dart to fix the dart. Don't let the tape entangle the blade except the base. 5. Use it carefully. Because this dart uses a real blade, throwing it at people or animals will cause serious harm. Only throw darts at boards, cardboard, foam and other inanimate targets.

method 4: 1, origami darts. After several folds, a square or rectangular piece of paper can be folded into a dart with four points. Use square origami or rectangular engineering paper as darts. Most folding methods and techniques are similar, but there are still some changes. If you want to make something different, just fold an eight-pointed dart. This kind of origami darts can be made of sticky notes. 2. Use paper clips to make darts. You can break two paper clips and tape them together to quickly make a simple four-pointed dart. 3. Make darts with binding rings. If you have an extra binding ring or a three-ring binder, you can make a metal dart by leaving two. 4. Make a dart with tape. Nowadays, tape can make almost anything, and darts are no exception. Use cardboard as the foundation first, and then wrap it with metallic tape. 5. Make darts with nails. Four nails glued together can quickly make a long-lasting four-pointed dart. 6. Recycle old CDs to make new darts. Trace lines on old CDs, and then cut them carefully. Note that such darts are more suitable for decoration than throwing. 7. Use old cans as darts. Carefully cut the cover and file the edge to make a simple and relatively real dart. 8. Use metal sheets to make darts. To make it more realistic, trace the appearance of darts on a thin metal sheet or steel sheet and cut it out.