*So you stopped and asked her what was happening to her crotch area only to see her looking back at you with the mischievous smile on her face.*

She's normally the sweet, caring and the loving wife until she gets horny and lets her cock to get erected, causing to form the growing bulge on her crotch area.

You were doing some yoga with her when her crotch area started to bulge until it eventually got bigger every second.