Symbolism, Imagery, Allegory
On top of all her other troubles, Pamela has some livestock-related anxiety. Like, when Pamela is plotting her escape from the Lincolnshire estate, she is terrified to hear one of the maids has had an accident involving one of the bulls in the pasture near the back door, which is on her escape route.
Then, during an aborted escape attempt, she's so keyed up that she mistakes two cows for their male counterparts—and believes that the beasts are possessed by the twin spirits of Mr. B and Mrs. Jewkes. Because … that kind of thing happens?
Here's the encounter in her own words:
Well, here I am, come back again! Frighted like a fool, out of all my Purposes! O how terrible every thing appears to me! I had got twice as far again, as I was before, out the Back-door; and I looked, and saw the Bull, as I thought, between me and the Door; and another Bull coming towards me the other way: Well, thought I, here is double Witchcraft, to be sure! Here is the Spirit of my Master in one Bull, and Mrs. Jewkes's in the other; and now I am gone, to be sure! O help! cry'd I, like a Fool, and run back to the Door, as swift as if I flew. When I had the Door in my Hand, I ventur'd to look back, to see if these supposed Bulls were coming; and I saw they were only two poor Cows, a grazing in distant Places, that my Fears had made all this Rout about. (47.11)
So, what's up with these bulls? Well, apparently they get all mixed up with Mr. B and Mrs. Jewkes in Pamela's minds, which makes us think that they're some kind of symbol of masculinity, specifically the dangers of being too close to unneutered masculinity. (Pamela describes Mrs. Jewkes as being pretty masculine—check out our Character Analysis for the deets on that.)
After all, Pamela's fears about being in proximity to the giant beasts seem to be allayed when she realizes they are girls . . . which is a bit odd, no?