The dead mice contain acetaminophen which is the active ingredient in Tylenol. If the snakes will eat them, they will croak. No major risk is supposed to be for other animals.
To assure the success, some details were attentively planed. The parachutes, built from cardboard and tissue paper, have a special design favoring the hung in the forest canopy. This is the place tree snakes attempt to aquire their food from. To have a feedback about this mission, some mice have data-transmitting rigs which work via radio.
The brown tree snake is infamous for being an invasive species which is responsible for devastating the native bird population in Guam. This snake can be very aggressive when confronted but due to the placement of the fangs the neurotoxic venom is difficult to convey into a bite on a human. Serious medical consequences are susceptible to children.
