Sentence:  The mare never moved; but after immense weight had been placed on both, the horse began to <WSD>sidle</WSD>, and before the last bag could be put on him, he sunk on his knees; it was put on the mare, and she bore it, never moving her posture until she was unloaded. 
Meaning of the word marked with <WSD> tags:  To (cause something to) move sideways. (from late 17th c.)