We captured and kept animals in the same way as during the recognition experiments described above. Snakes were fasted for at least 5 days and anurans were fasted for 48 hours prior to the trials. We only used females and juveniles in the experiment. We marked each animal with a visible implant elastomer tag [62]. We placed the red banded snakes, bullfrogs, and each of the native anuran species into separate ponds for one day to habituate them to their new environment. We then randomly assigned animals to ponds according to the treatments. We checked to see whether any anuran individuals were hunted by the snake or bullfrogs in each pond every night (1930 h–2330 h). Observers with a 12 volt DC lamp entered the pond to carefully determine whether any anurans were lost from a pond. When native individuals were missing, we would induce the snakes to regurgitate to recover prey items from the stomach [63] or flush the stomach contents of bullfrogs with water [64]. We only induced snakes to regurgitate when bullfrogs were missing. We then replaced the consumed individual with a new one (of the same species and with a similar body size) into the pond to keep a constant availability of bullfrogs or native anurans. Bullfrogs whose stomachs were flushed were also replaced with new ones to remove the effects of flushing the stomach on the anti-predator behaviors of the bullfrogs to the snake. Stomach contents were identified to species. Prey items in the stomach contents were weighed to the nearest 0.1 g. The experiment lasted for 21 days from 24 September to 15 October 2008.
http://plosone.org/article/info:doi/10.1371/journal.pone.0024299#article1.body1.sec2.sec5.p2

This control protocol represents nothing the snakes would typically experience and its effect on their behavior is completely elided.