Hold him gently between his legs and gently press his nose for a few seconds (be sure to grasp the time). As soon as he lets go, he will open his mouth by himself, then gently break his upper and lower teeth (the longest two) with his hand, pull out the needle with a needle tube and squeeze the medicine in. Be sure not to spray it into his trachea when taking medicine, so he will feel very uncomfortable; Don't push too hard all the time, or he will be particularly nervous and even more unwilling to cooperate next time.