In the scene in "The Dog Park" where Mr. Bleakman is talking about the rare bird while walking through swamp grass, his mouth doesn't move.
In the scene in "The Dog Park" where the dogs talk about playing fetch, Mac's collar turns black at one point.
Mac: (as Cleo and T-Bone play tug-of-war) Go, Cleo! Go, T-Bone! Go... Cleo!
Cleo: Hey, whose side are you on, anyway?
Mac: On the winner's side, of course.
Mrs. Bleakman: It's just Clifford. Is that a problem dear?
Mr. Bleakman: No problem at all.
Mrs. Bleakman: No dogs, no laughing kids or playful squirrels, no kids and squirrels, no lady to feed the chirping birds. It certainly does make the park quiet, doesn't it?
Mr. Bleakman: Violet, where's everybody: the kids, the birds and the squirrels?
Mr. Bleakman: Get this galloping gargantuan out of my face.
Cleo, T-Bone and Mac: Red rover, red rover, send Clifford right over .... Maybe this wasn't such a good idea. Get out of the way!
Mr. Bleakman: There oughta be a law about dogs in the park.
Mac: You know, I thought having my own club was going be more fun than this. Oh well, at least I have snacks.
Mac: I can't believe Cleo won't join the club without (disgusted voice) T-Bone.
Mac: Not everyone can get in, you know.
T-Bone: The shuffle-dog champion of the, uh, universe steps up.
Clifford: Ten points.
T-Bone: Way to go, Cleo.
Cleo: It's a gift.
The character Porcupine in the show Franklin did the exact same thing as Mac did in "Mac's Secret Dog Club" to the characters Snail and Franklin in the episode "Franklin and the Secret Club." In that episode, though, everyone was willing to be a member of Porcupine's club, even though they knew that Franklin and Snail would be left out.
Clifford's Big Idea: Be Truthful
Speckle Story: Speckle and the Really Great Book