Before George and Lennie arrive at the ranch, the two men camp out on a peaceful riverbank. George then recounts their dangerous experience in Weed and instructs Lennie to travel to the riverbank and hide in the brush if he is in serious trouble. In chapter five, Curley's wife befriends Lennie while he is alone in the barn and begins to have a conversation with him despite his reluctance. Lennie then discloses the fact that he enjoys touching soft things and Curley's wife allows him to stroke her hair. Tragically, Lennie is too rough with her hair, which causes Curley's wife to panic and scream. Lennie is alarmed by the entire situation and accidentally kills Curley's wife by breaking her neck. Lennie understands that he has done something terrible and recognizes that he is in serious trouble. He then recalls George's advice to hide in the brush by the riverbank and says to himself,
"I done a real bad thing . . . I shouldn't of did that. George'll be mad. An' . . . he said . . . an' hide in the brush till he come. He's gonna be mad. In the brush till he come. Tha's what he said" (Steinbeck, 45).
In the opening scene of chapter six, Lennie cautiously walks towards the riverbank like a "creeping bear" and quietly drinks from the pool of water. Steinbeck then writes,
When a little bird skittered over the dry leaves behind him, his head jerked up and he strained toward the sound with eyes and ears until he saw the bird, and then he dropped his head and drank again (50).
Lennie's reaction reveals his fear of being caught and suffering the consequences of killing Curley's wife. The sound of the bird quickly moving over the dry leaves draws Lennie's attention and he immediately thinks that someone has followed him to the hiding spot. When he discovers that the small bird is responsible for making the noise, he relaxes and continues to drink from the pool of water. Essentially, Lennie realizes that he is no longer in immediate danger after spotting the bird and was simply frightened by the noise of the dry leaves. Steinbeck goes on to describe Lennie's actions by writing,
When he was finished, he sat down on the bank, with his side to the pool, so that he could watch the trail's entrance. He embraced his knees and laid his chin down on his knees (50).
Given the fact that Lennie is mentally-disabled, he probably does not recognize the gravity of the situation or realize that Curley will want revenge. He also does not understand that he will be wanted by the authorities and his immediate concerns are about how George will react. After Lennie finishes drinking from the river, he says to himself,
"George gonna give me hell . . . George gonna wish he was alone an' not have me botherin' him" (Steinbeck, 50).
Overall, Lennie's quick reaction to hearing the bird skitter over dry leaves reveals his concern that he has been followed and discovered. Lennie understands that he has done something terrible and does not want to get caught, which is why he scans the area before continuing to drink from the pool.