Catfacing is a deformation which appears in some tomatoes, strawberries, and stonefruits. Contrary to what you might expect, it does not actually cause the face of a cat to appear in a fruit. Instead, the fruit develops tannish scars which run along the blossom end of the fruit, and sometimes extend into the cavity of the fruit, rendering it largely inedible. Catfacing is not dangerous, but it is irritating, and it can reduce the sale value of a fruit.
Usually, when a fruit develops catfacing, it starts by pucking and scarring, and it may also develop deep cracks. The catfacing radiates out from the area of the fruit where the blossom used to be, and if it is especially bad, it can wrap all the way around the fruit. In the areas of scarring, the fruit is woody and inedible, in addition to unsightly, and many people regard catfacing as a turn-off when it comes to buying fruit as a result.
The causes of catfacing are not fully understood. Exposure to low temperatures when trees and plants set fruit appears to be a factor, as the temperatures encourage the blossoms to adhere to the fruit as it develops, rather than dropping off. Plants which are underpollinated may also develop catfacing. Extreme heat may also be linked with this deformation, along with drought, which stresses the parent plant. Some crop pests also appear to contribute to catfacing.
Catfacing is more common in heirloom variety fruits, and in plants bred to produce especially large fruits. It is such a widespread problem in heirloom tomatoes that many people are under the impression that some catfacing is to be expected when purchasing heirlooms; if your grocery store or farmers' market carries heirloom tomatoes, you can probably find some great examples of catfacing in tomato season.
There are a couple of things gardeners can do to reduce the risk of catfacing. Keeping plants well-watered and fertilized is a big help, as it keeps the plants strong and healthy while fruit develops. Protecting fruit from cold temperatures with cloches or covers is also highly advised if there is a cold snap. Crop pests can be controlled naturally with the use of companion planting, or with pesticides which target such pests. Care should be taken when insects are assumed to be the cause of catfacing, as a wide range of insect pests can potentially cause catfacing, and they may not all be controlled with the same plants or pesticides.
