Blood samples

[Lady Birb]

This would also make changeling rounds more interesting. The original sample could out the changeling, but could easily be tampered with to frame others.

I don't think the blood samples should be able to show if someone is a changeling. Too much turbonerd potential. If you want to bloodtest someone, you need to manually draw their blood, which puts you at risk of being stung. For lore reasons we can say that a changeling snuck onto the station, absorbed someone, and assumed their identity after blood samples were taken but before the start of the shift.