Planting fake evidence

The old man wanted to fap some fresh semen into her hole, possibly while slipping his tip in, but it was too risky to do so... he should at least make her cum for another few hours if he hoped to pull off something like that without her noticing!
Even then he wanted to take the challenge... but even if he did and managed to pour a fresh load in, by then it'd be too fresh to be used as proof!
Maybe she'd be too out to recognize such a simple thing and would have to suck it up, but what if she reneged once she came back to her sense?

Better to plant some fake evidence now and make her recognize her "fault" now and then have her cum her head out so she couldn't ponder too much about it.

He led her to the bed and let her lay on her back, the change of location giving the girl some of her wariness back despite still being a bit high from all the orgasms... however he didn't make any strange move, though some may argue simply telling her to lay on the bed and spread her legs was problematic enough on its own.
Still, she was in the same position as yesterday when he made he cum for a whole hour straight with the excuse of treatment, and once she gathered enough resolution to ask why she had to move on the bed he shut her off saying that it'd be more confortable for her to lay down during treatment.

Was he still not done?
Mei didn't know that if it wasn't because it was about dinner time, yesterday his treatment wouldn't have lasted for only an hour... today however they began immediately after lunch at noon, and while more than an hour had gone by it was still early afternoon. Dinner and Ren won't come anytime soon, and if it wasn't because he had some scruples she wouldn't know just how fucked she'd be!

But regardless of what she didn't know, spreading her legs as the old portly man kneeled between them and cupped what should have been her most secret and precious spot still made her feel a great deal of shame, even more so when said old man had gotten her to squirt so many times and will most likely continue to do for the rest of the day!
Despite herself, she felt her pussy tingle in anticipation and she barely restrained a gasp when he began to flick her clit with his fingers...

She closed her eyes in an attempt to deny the pleasure and Old Mo took his chance to dip his free hand into a jar at the side of the bed, scooping out a large amount of the spunk he unloaded in there last night!

A large amount of it was coating his index and middle fingers, which immediately burrowed into Mei's pussy!
The clit flicking distracted her enough to not notice the extra-sliminess on his fingers, and she was feeling too good to notice he was smearing hes precious place with his seed... her love juices would diluite some of it, but after repeating the process a few times he got enough in to look like she was dripping some residual from last night's fun...

Great!
Now all that was left to do was complain to her about it and abusing his power as the owner of the house and her doctor to bathe her from now on.
Or... she could use that as leverage to get some sexual attention... either way, he could still plant more evidence another day!