Many people find cruelty toward animals abhorrent, that is, they think it's detestable, obscene, repugnant, repulsive, and offensive to the mind. In other words, they really, really don't like it.
When you think of abhorrent, think of horror, as in something so vile and loathsome that you can only react to it in horror. In fact, the word abhorrent in Latin means “to recoil (back away) in horror.” Note that the ending is spelled -ent with an e, not an a. Maybe the a found abhorrent so abhorrent that it didn’t want to appear in it a second time.