The aliens on the spaceship have faces with two eyes, much like humans. Yet when Frisby describes his encounter later, he describes them as having one eye in the middle of their foreheads. This is consistent with his character's reputation for being an unreliable narrator.
When Frisbee is being interviewed aboard the spaceship, he mentions Princeton University and one of the aliens appears confused and says "...you mentioned Princeton. It's my understanding that you went to the University of Wichita" but earlier that same alien was told that Frisbee "...studied in most of their major universities" so he should have already been familiar with the fact that Frisbee claimed to have gone to more than one school.