Can dogs fake injuries for pity?

I have two dogs. The male has bad hips and limps around and gets "special" treatments because of his disability like being carried or lifted places, and I massage his hip muscles when I can. I try to treat my female equally, (she gets peanut butter when I give him some for medicine and she gets pets after his massage) but she doesn't need to be carried or lifted onto the couch and bed.

I have noticed my female get's irritated when she does not get the same treatment as the male. Recently she has started limping, and after watching her I noticed she switches feet like a child trying to fake it.

Do dogs have the mental capacity to understand why one receives special treatment and fake an injury to get the same?