Glass vial snapping

I cut my finger while trying to firmly close a teflon-lined green screw-cap onto a 4 mL (1 dram) glass vial. The vial and the cap were ordinary products commonly used in labs.. Unexpectedly, the vial broke in my hands and cut my left thumb, causing significant bleeding. Thankfully there was no chemical contamination onto the wound because the vial was clean at the broken part. The finger was dressed with medical tape and healed over several weeks. I speculate that the vial had a crack somewhere. The lesson is to close the vial slowly and gently, instead with a jerky motion and too much force.