ELI5 Ballpoint Pens - why do the caps have holes?

Why do most pen caps have holes? When a pen quits half way through the word, why will it write on a fresh piece of paper but not over the letter it failed on? Why do some people call the ball point pen a biro pen?   ... We explain like i'm five!   Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: smalltownmortician, sonderfrission, conspiratorm & capilot For some cool science experiments to do with dry ice, check out this site: https://dryiceinfo.com/science.htm To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]