[Despite his stature, the kid in question is surprisingly agile - he scampers right along, more or less keeping pace with the lanky grown man he's chosen to ally himself with. Though he is breathing much more quickly, too. Little lungs gotta work hard.]

H-- How dare you!
He may be tall, but he is nothing I cannot handle!

[Apparently height is a bit of a sore spot. Zim points accusingly at Spike, as he continues.]

You are tall and yet you needed my assistance to escape! Clearly, you humans don't correlate height and greatness!