Hint
A citrus fruit is mentioned five times in the article's text.
What word, covered by a red rectangle, completes the terrible pun on the Magic: the Gathering card at left?
Hint
The rather improbable subject of the pun is penmanship.
Solution
Cross the eyes and you'll dot its teeth. (The pun is on "dot your i's and cross your t's.")
Congratulations to yesterday's solvers Jacob C., Nico, Yana, Charlie, Inca, Maddy, and Mr. Gregg. Thanks to everybody who made a guess!
Ten years later, Dr. Shapiro revived Puzzle of the Day at Proof School, writing each day's puzzle on a name tag. After 600 puzzles or so, he was just starting to feel normal about students reading his chest all the time when campus closed and the puzzle, like the rest of our lives, moved online. New puzzles are posted daily on school days.
Want to catch up on old PotDs? There's an archive currently containing puzzles from March to June 2020.