When this episode was shown on Noggin, the Noggin logo at the bottom-left corner entirely blocked out the view of the pawprint on the 2nd clue (a wolf) until the camera angle changed to focus on it.
The 1st clue (bricks) had multiple pawprints on it.
In Blue's photo album that Steve opens up, the picture of Mr. Salt and Mrs. Pepper was taken from the series premiere episode Snack Time, and the picture of Tickety Tock is from the episode What Time Is It For Blue. Also, Magenta is first mentioned and shown in pictures of her and Blue at school in the album but doesn't appear until the episode Magenta Comes Over, in which the picture of Blue and Magenta painting was later added in the yellow swirl frame in that episode.
Shovel and Pail's first appearance.
This is the first episode where Steve and Mailbox have a conversation during the Mailtime segment.