I've been watching videos on youtube and a few of them mention having Petri dishes under hides, what's that for

2.0 Border Collies - Jinky and Chance
3.0 Cats - Monty, Dodger and Crunchie
1.1 Royal Pythons Orlina and Sedrick
0.1 BCI Boa - Aasia
1.0 Western Hognose - Hagrid
0.1 Bearded Dragon - iiara