Does the professor remember when he threw one of the rabbit-cat-bird critters at Merlin's face and laughed at the ensuing chaos? Because Merlin remembers. And is repaying the favor right now by bursting into laughter of his own upon seeing the man's predicament.

For a famed wizard who's over a thousand years old, he sure can act pretty childish.

And yes, that same critter is apparently still following Merlin around, though the mage is continuing to pay it no mind whatsoever.