In the jungle an elephant walks aggressively

In the jungle an elephant walks aggressively; he meets a lion and asks him:
“Why are you not as big as me?”

And he, making himself small:
“I don’t know” and quickly leaves.

The elephant then meets a rhinoceros and says,
“Why aren’t you as big as me?”

And the rhinoceros also first answers “I don’t know” and then runs away.
Finally he sees a little mouse and thunders at him too:

“Why aren’t you as big as me?”
And the little mouse: “When I was little I was very sick..