Evaluations of the cats' facial and behavioral reactions to different concentrations of L-proline and quinine monohydrochloride (QHCl) as well as mixtures with different concentrations of L-proline and QHCl were performed. The cats were offered one of the solutions and a control in a 5-min two bottle preference test. The cats were videotaped during the tests and their behavior was analyzed using Noldus the Observer XT. In total, 50 different behaviors were evaluated. Each of the 13 cats was tested with each stimulus combination twice. Data were analyzed using a Wilcoxon’s test for pairwise observations, ɑ = 0.05.

• Experiment 1: five concentrations of L-proline versus water.
• Experiment 2: five concentrations of QHCl versus water.
• Experiment 3: five concentrations of a L-proline and QHCl mixture versus an L-proline control.