Our cat Felicity has recently developed a weird growth at the base of one of her ears. It started as a red blistery thing, and has grown a conical crust. As you can see from the pic, it's not at all pretty to look at, and I was just wondering if anyone could identify its likely cause.
If it doesn't heal up I will take her to the vet's, but if someone here says "that's serious - get her to the vet's right now!", then obviously that vet's trip will have to take place sooner rather than later.
She doesn't seem to be at all bothered by it and is fine in herself. If it's relevant, she's anywhere between about 15 and 17 years old (we're not sure of her exact age but she is getting on a bit by cat standards).