Researchers have found that not only does your body’s microbiome (bacterial ecosystem) thoroughly mark a room to make it your territory within hours, its signature of bacteria types can be used to identify you and where you’ve been better than fingerprints. They also recommend having a family dog to help establish a child’s microbiome by passing bacteria from family members and friends. The richer the bacteria population, the stronger a person’s immune system becomes, and the fewer the allergies.
I think Missy has a transmat. And a gardeny TARDIS. She’s been following the Doctor saving people seconds before death. People the Doctor thinks are dead are saved in Missy’s TARDIS thinking they’re in Heaven because the Doctor killed them.