Port knocking is an authentication technique used to open closed ports which are behind a firewall. It is mainly used to prevent hackers from doing a port scan and is one of the security measures a network administrator takes to secure the network.
Yes, it is safe to swim while you on periods. Period blood doesn't flow outside the vagina like it usually does due to the counter-pressure of the water. But You still need to wear some a tampon or a menstrual cup to avoid getting into a sticky situation.
Resin tooth filling typically contains a filler particle such as quartz, which provides the mixture's strength and color. It is costly as compared to silver tooth filling.
In some cases, the change in period blood color can indicate a health problem like fibroids, low estrogen levels, and even vaginosis.