Thomas, Chess, Birch, Hertzig and Korn showed that "easy" babies readily adapt to new experiences, generally display positive moods and emotions and also have normal eating and sleeping patterns. "Difficult" babies tend to be very emotional, irritable and fussy, and cry a lot. They also tend to have irregular eating and sleeping patterns. "Slow-to-warm-up" babies have a low activity level, and tend to withdraw from new situations and people. They are slow to adapt to new experiences, but accept them after repeated exposure.