You eat like a pig.

Pigs acquire, through learning and evolution, expectations of their environment. Frustration of expectations results in motivation to change these conditions and is therefore adaptive. Initially, frustration should produce problem solving behaviour. If these responses are unsuccessful, other behaviours, reflecting general frustration should be elicited. Our purpose was to study both types of responses to frustration in grower pigs.

So these scientists took 18 pigs, and fasted them for 1, 2 or 3 hours every morning. On Monday and Tuesday the pigs got full feeders BUT on Wednesday and Friday they got 2 types of feeders – lidded with the lid bolted down (L) and un-lidded that was empty (O). Results showed that pigs in pairs showed an increase in sitting and playing and single pigs started to ignore the L-feeders after 2 hours while increasingly looked into the O-feeders.

from “Frustration of goal-directed behaviour in swine”, N.Lewis in Applied Animal Behaviour Science, Volume 64, Issue 1, p 19-29