Any guidance regarding thumbtacks and pushpins?

I was tossing around ideas for creating shoespikes just last night, using the community’s guide… as a reference. the referenced community page While I understand scenarios place a big emphasis on imagination, I felt similarly about shoespikes (usually I wouldn’t consider cutting yourself or piercing sharp objects into your skin “sensible”, yet I do enjoy mild pain). From what you’ve experienced, is there a “safe length” that can pierce the skin, or is it generally safe as long as you stay within your tolerance limits? Also, which other situations/body parts would you recommend for using drawing pins, and where should they be avoided (e.g., genitals, inside mouth, away from face etc)?

Here’s what I did: I cut two cardboard sheets into the shape of a shoe sole, then placed newly bought flat-based drawing pins underneath. I held off on using tape because the shoes are still in regular use. After compression, the pricks extended about 2mm outward, which was enough to feel the sharp points and light pain. However, since it was my first time, I hesitated to take too many steps or increase the spike length. Any other tips that I might have missed are very welcome. I want to be as safe as possible when trying this next.