I have given my Insect 4 horned fruits, and my rat just ate cheese. My insect has only gotten 1 stat up and the cheese
gave no stats, am I doing something wrong?

It requires a certain number be eaten for each increase.

After 3: +1 random stat
4 more: +1 random stat
5 more: +1 random stat
Etc.

So the rat needs two more cheese to get to the first breakpoint, and the insect would need three more fruit to get to the second breakpoint.