My father-in-law is helpless but his is always hardening

When my father-in-law called me because his pants were wet from the shovel, I quickly walked over to him to clean and change his wet pants. But while I was wiping his crotch, I was startled by something that suddenly stood upright and hardened between my father-in-law's crotch. His seemed to harden and made me want to suck it. But who would have thought that my father-in-law, who looked helpless, actually invited me to have sex. Without any resistance from me I immediately shook his already tense. Then it all ended happily my father-in-law's sperm cropped in my mouth and it tasted deliciously sweet