How old is the gecko you gave to these people? If it's a baby/juvi it's probably just frightened. I've noticed that the older some gecko's get, the less they put up with being disturbed and therefore sometimes get angry and bite..
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Reptiles:
2.2 Leopard Gecko Morphs
1.0 Bearded Dragon Morph
0.1 Box Turtle (Rescue)
0.1 Albino Ball Python (BHB line)

Bird:
0.1 Jenday Conure

Pups:
1.0 Black Lab/Pit Bull
1.0 Maltipoo

and lots of tropical fish!

-Patrick