I had
this little Dude (see link) slither past my keyboard whilst I was at work. We'd left a ceiling tile out in the office, and didn't clean up. Having lived out in the boonies all my life, I just stayed dead still as he went past. No worries.
It was after 5pm on Friday, and nobody was answering the phone. So I just stuffed some pillows under the door, put a sign up, and emailed the other office staff.
We never saw him since.