Summarize this article in one sentence.
One common sign is a lump in its neck. There are also several things that a horse will actually do when it is choking. Despite showing these signs, be aware that a horse may still try to eat or drink.  Coughing Yawning Arching neck Drooling Difficulty breathing If you are not the horse's owner, contact the owner to let them know about the situation. Choke will get worse if a horse continues to eat and drink, so do your best to keep the horse from any potential food and drink sources.  Move the horse to a stall that does not contain any bedding. The horse may want to eat the bedding, so it will be important to remove all potential food sources. A horse will become dehydrated quickly, but do not to allow it to drink water from a bucket. A horse may become increasingly anxious and restless if it is choking, which could put you in danger of injury.  Do not approach the horse if your safety is at risk.  If necessary, the veterinarian will sedate the animal to calm it down. This will help prevent food from going into the horse's airway, which could cause respiratory complications.  Keeping the horse standing will also keep it from giving up, which could easily happen if the horse lies down. If you have a head-collar/halter on hand, use it to hold the horse and keep it standing. However, do not attempt to hold the horse if your safety is at risk. The lump will indicate where the food has become stuck in the esophagus.  Do not touch the horse's neck if the horse is too restless or anxious to approach.   If the horse will allow you to touch its neck, try to gently massage the lump to assist in its removal. If the object is something soft like an apple, it will dissolve after 5-15 minutes. If it is not gone by then, it will probably be something harder or more dense, like a carrot. Blockages can also occur from dry foods such as sugar beet. If not soaked properly, dry foods will swell and cause the same result. This can only be removed by the assistance of a veterinarian with proper equipment.

Summary:
Look for common signs that a horse is choking. Call the veterinarian immediately. Prevent the horse from eating or drinking anything else. Keep the horse as calm as possible. Keep the horse standing with its head down. Touch the horse's neck to find the lump.