Robert did see Corner shutting the cabinets. He didn't think much about it. He cast a slightly amused look at Corner as if to say What? Surely you didn't expect different, did you?
Robert was honestly trying to act as he hoped his patients would act--or somewhere thereabouts. What interfered was that he had this crap on his brain that vexed him, things he needed to solve. First on his list was the damned goo eating his foot. Second was getting up and getting back to work. As long as these potions were out and about, people's lives were at stake.
He knew his own work better than anyone. He expected himself to, but it frustrated him that someone else was studying him closely enough to see even the most minute details of his potion making. That was unnerving.
He wasn't afraid for himself, but it did make him wonder if someone were perhaps aiming to strike out at him through others, whether it was just the public in general or whether they would strike out at his loved ones. He wasn't about to do nothing. Corner's earlier suggestions of being reasonable about it aligned with Kate's feelings. Robert honestly didn't know how to live with himself if he did that.
Corner didn't need to know where that came from for Robert, but the wound ran deep and long, and it was in the very foundation of what had formed the making of the somewhat enigmatic man he'd become.
He'd pushed the memory away repeatedly, deeply, since he'd been a small boy. Remus had been just four. Robert had been only five. They'd shared the same bedroom. Robert had been awakened by the sound of someone coming in through the window. Terrified, he'd scrambled under the bed and he'd hid back against the wall.
In the moonlight, he watched the horrid creature come through the window, make a sweeping scan of the room and then land his sights on Robert's bed. He'd thrown back the covers and hadn't found him. He'd spun around and saw Remus still asleep and unaware. Frozen in utter terror, Robert saw the monster open its jaws, saw its huge claws reach for Remus. At that instant Remus had awakened and had started screaming.
The hideous screams of his brother's horror and anguish had brought Dad, but not before the creature had bitten Remus, changing everything forever. Robert remembered his father driving off Greyback, remembered his mother racing in and panicking over the life altering wounds on her youngest son. So preoccupied with Remus were they that neither of his parents had given thought to where their other small boy even was.
Robert didn't actually know how much time had passed, but he remembered it had gone from night to just before sunrise when his father found him under his bed. He'd pulled Robert out, chiding him harshly for frightening his parents so by disappearing for so long. They'd never asked him if he was alright. They'd never hugged him and reassured him. What they had done was to tell him, sharply, to 'sit on that bed and think about what [he'd] done.' The boy had thought that what he'd done, not making the monster go away, was the mistake. Robert's mistake was never spoken of again.
As a father and a grandfather, Robert could now understand that fear that caused a parent to react in anger at that sort of fear. The boy he'd been didn't understand it. The boy grieved at the loss of who his brother had been before because the wound so changed him and grieved at the distance he had now with his parents, largely on his own part because of the weight of the new responsibility he had, with no clue how to carry it out. The boy had never ever let go of the feeling that he'd failed, that he'd been responsible to do something to protect his brother, that all the suffering his whole family were destined to go through would always be something they would blame him for.
He'd never talked about it, not ever. He'd had decided somewhere while Remus was still recovering from the bite wound, that he would never let that happen to anyone he loved again. By the time he'd entered Hogwarts, Robert was a closed boy, afraid of little, quiet, blunt, sarcastic, outwardly logical and analytical. His father had expected him fully to be a Ravenclaw because he was always learning something. He was interested in anything that, for him, connected with life--plants, biology, healing, etc. "That bloody dumb hat," he'd thought, had buggared it and made him a Gryffindor, and his parents hadn't understood why either.
And so, here he was, decades older, the boy long gone, so far as he knew. Corner was right, of course, that there were others that could and should be doing the hunt for tainted potions, and in fact, there were a few. It didn't negate Robert's own drive to resolve it for himself. He was fully prepared for Corner to not understand him, and he was equally prepared for whoever decided not to like him to go ahead and do so. It complicated his life less when someone distanced themselves.
What he didn't deal with well was anyone getting too close except for those to whom he'd give that right, which were few and far between. If Corner decided he were put off by Robert's choices, then, well, that would work out well for Robert, wouldn't it? No prying would be involved.
Actually, all Robert had to do was weather this out because, in reality, Robert didn't have a regular healer of his own. He hadn't had a regular healer for himself since he'd boarded the train for Hogwarts. He normally attempted to either deal with it himself, get a friend to help him, or settle for whoever was on duty at St Mungos at the time. It made for cursory relationships, and he was fine with that. He didn't expect this time to be any different. He didn't expect that Corner would want to be involved any more than anyone else had. Even Terry appeared to be getting into that uncomfortable mood that was remedied by a bit of distancing.
"I'll leave you to it, then," Robert said to Terry, wanting to let him off the hook as soon as possible. "Its the second door on the left in the sub basement. You'll need the password too, in addition to the key. Today's password is Fluxweed. Good luck."