Human females become the most feared aspect of humanity when aliens realize that they regularly bleed once a month as part of their reproductive cycle. -- YizukiKhons
When venturing into the wild spaces, those territories outside of the Galactic Alliance, it is vitally necessary to have at least one human on the crew. Their pack-bonding and protective capabilities were highly prized in wild space.
Such was the case with the TikTavi, where the ship's human had a name unpronounceable by the crew. She let them call her Tutu, and for most part, her peculiar biology was something she managed for herself.
Humans, they learned, got bored when nothing new was happening. In the spaces between destinations, the human socialised, played games, and generally wandered everywhere like the random element she was.
T'k'tur had the job of attempting to keep the human out of trouble. A difficult enough task when they were 'adventuring', but there was little more troublesome than a human when they were bored.
Trouble arrived today with blood. T'k'tur felt this was necessary to mention. "Have you harmed yourself, Tutu? You are bleeding."
Tutu looked down at her pants. "Aw shit," she muttered. "I never get any warning. I'll be back when I have this sorted. And new pants."
T'k'tur waited patiently for Tutu's return. When she did, she indeed wore a fresh set of pants. "Your wound is organised, yes?"
Tutu rolled her eyes and sighed, "Oh boy..." She examined the ceiling for answers, and finally found them. "Human biology has no seasons," she began. "For humans, especially females, there are things we can't control. Including the time that we shed our uterine wall."
"Uterine?" echoed T'k'tur.
"It's like your seasonal shed," she tried. "Only, inside... and for just one organ."
"Is most uncomfortable?"
"Oh yes. Tomorrow, I'll feel like something is trying to escape."
"Must to be grateful, is yearly occurrence, yes?"
"Uh... about that... It happens once every twenty-eight days. On average. I have an irregular cycle so... For me? Ignore the twenty-eight days. It's... random."
"Twenty-eight days is not enough for recovery!"
"I'm glad you sympathise. Really."
But in her next escort job, Tutu found that the aliens who hired her got incredibly respectful. Word got around, and legends perpetuated. Hell, they fissioned.
Just another one of the tall tales about humans.