Board Thread:General Discussion/@comment-32455678-20170702063923/@comment-27136653-20170804211839

Undyne isn't determined because of some tea. She is just that. Determined. I don't know from where did you get this idea that a golden flower tea gives her determination.

And DT is most likely yellow, since everything related to DT is yellow too:

http://nochocolate.tumblr.com/post/157954943241/determination-is-yellow

So if you acknowledge the fact that the red stuff is ketchup and Toby colored it because he wanted to further emphasize the moment (we all first thought that it was blood), then there's not much proof for Sans being injected with DT. In fact, he might be fighting you because he's actually scared, since such thing has already happened, and he most likely didn't do anything about it back then. Read his dialogue during the battle. He says that this is how things end up when people like him don't do anything. As IF it has already happened once. That may be the true reason why he actually wants to fight you.

And don't say that even if he wanted to fight you, he wouldn't have any DT for that. Because that's bullshit. Even the weakest, wimpiest monsters try to fight you here and there, so if Sans gets a reason to fight you, he WILL do it.

Monsters don't need doses of determination to do anything, they can summon it on their own!