Some teachers worry that using red ink to grade a paper seems harsh, that it might hurt a student’s feelings.

But the real problem with red pens may be what they do to teachers.

Participants in a new study were asked to grade two paragraphs written—they were told—by a student learning English. The 103 participants were randomly given either a blue pen or a red pen. The result: Those given red pens marked significantly more errors.

In another experiment, students were again randomly assigned blue or red pens and asked to grade a one-page essay on a scale from zero to 100. The median grade assigned by those with blue pens was 80. The median for those with red pens was 76.2.

There’s more. In a third experiment, participants were asked to fill in the remaining letters in partial words. The partial words, however, were carefully chosen by experiments so that they could be completed either as words associated with error (like “fail”) or simply neutral words (like “fair”). Guess what? People with red pens were more likely to choose words like “fail.”

Here’s what the authors think:

Red pens, ubiquitous in academic settings, are not inert objects; they are laden with meaning. By virtue of their strong association with failure and error-marking, red pens can change the ways teachers correct student work.

If you read enough so-called priming studies like this one, it’s hard not to come to the conclusion that we are ridiculously suggestible creatures influenced by the tiniest, most trivial details. Not sure how this study relates to the recent finding that men who wear red shirts are more attractive to women.

(You can, for once, read the full paper here. The title is “The Pen Is Mightier Than the Word: Object Priming of Evaluative Standards.” The authors are Abraham M. Rutchick, Michael L. Slepian, and Bennett D. Ferris.)