Moonbeam (Simile)
"The moonbeam was like a silver blade slicing through the room on to her face." (9)
The moonbeam is shining so brightly into the room that it illuminates Sophie's face very brightly when it falls on her.
Houses (Simile)
"The houses looked bent and crooked, like houses in a fairy tale." (10-11)
The houses that Sophie and the BFG pass on their initial journey to giant country look crooked. This may be due to the speed at which the BFG is travelling.
Dream Jar (Simile)
"He took something out of it [the suitcase]. It looked like a glass jar, one of those square ones with a screw top." (13)
The BFG reveals his grand secret to Sophie. He collects dreams in glass jars and he finally shares a secret with this little human who could pose a grave danger to him.
Arm (Simile)
"This was followed by an arm, an arm as thick as a tree-trunk..." (16)
Sophie compares the size of the BFG's to that of a tree trunk. This allows the reader to better envision what the giant looks like and the sheer scale of his size.
Giant's Leg (Simile)
"She was being bumped against the Giant's leg like a sack of potatoes." (19)
Sophie is being bounced against the giant's leg so much that she feels like a sack of potatoes. That is, like a bag of vegetables that is thrown around willy-nilly, without much regard for how bruised the vegetables get.
