u/Fun_Background_361

Between the time of 10 hours(from finishing custards to sleeping), a high rise his metabolism due to him being the biggest out of all the rest(hence why he turned infected more early).

Him killing the rest of the Teletubbies post-infected, due to the still continuous metabolic process due to Noo-Noo's infection of the custards. There is still an increase.

As he turns to Tinky Tank, he "evolves"(could be headcanon), increasing muscle mass and size at that moment as he "consumes" the last custard in the mainland. This is the peak of his metabolic activity until.

There is a potential decline due to the lack of source of food, which causes his metabolic activity to decline beyond the ending of Slendytubbies 3(which may end up killing him).