Many common pain medications that are safe for humans (and other species) are potentially fatal to cats. These medications include Acetaminophen (Tylenol, Atasol, Paracetomol etc.) Acetylsalicylic acid known as ASA or by the brand name Aspirin, and Ibuprofen (Motrin, Advil etc.) 

One extra strength Acetaminophen tablet can kill a small cat.

Only painkillers that are specifically prescribed for your cat by a veterinarian can be given when your cat is sick or injured.

Seasonal Warnings
Christmas Warnings
Remember: 
Mistletoe, Holly, Poinsettas and other Christmas plants are poisonous to cats. Christmas tree lights and electrical cords can cause fatal shocks and/or burns to cats that chew on them. 

Loose cords can entangle pets, leading to choking hazards, or the possibility of the pet accidentally pulling over the  tree or other decorations. 

Holiday foods such as chocolate, alcohol, nuts and spicy sauces can be toxic and cause Internal problems. 

Bones and plastic food wrap can cause choking and/or obstruct a pet's digestive system, and may require surgery. 

A big thing to be aware of is ribbon especially tinsel. It can cause serious  internal problems if swallowed. 

Any open flame is a potential burn hazard. Keep pets away from candles, fireplaces and any other open flames. 

Be cautious about dressing pets in holiday-related costumes. 

Keep pets safely in a closed room while holiday guests are coming and going from your home to avoid them getting outside.

Every year around Hallowe'en shelters and rescue groups stop all adoptions of black cats. This is because of the historical connection of black cats with "witches" and rituals, black cats are in danger of being picked up by people for ritual torture or sacrifice. Black cat owners also need to be especially aware of this phenomenon, and if they have outdoor cats keep them inside around Hallowe'en.