No, nothing about perf. The story goes that the printing plate was damaged (in some way) and the person who repaired it put something in that didn't belong there.
I'll call that correct. The number 2 was damaged in 3 places on the plate and the number 5 was inadvertantly placed on the plate as replacements. All red stamps of this era were 2c by convention. So there were sheets with a double error and sheets with a single error. The stamp is an error of denomination. There was a Scott 467, 485 and 505 error from the same printing. Your turn to post Sarah!
Nope. You'll have to look really carefully. Its a small detail, very easy to miss. Hint: three of four stamps are proper, only one is missing the detail. Try comparing them
The girl on the left of the crest has a sardonic expression on her face on this stamp, whilst she is quiziccal on the other three???!!!