Verb fall behind has 2 senses
  1. fall back, lose, drop off, fall behind, recede - retreat
    --1 is one way to regress, retrograde, retrogress
    Sample sentence:
    Somebody ----s
  2. lag, dawdle, fall back, fall behind - hang (back) or fall (behind) in movement, progress, development, etc.
    --2 is one way to follow
    Sample sentences:
    Something ----s
    Somebody ----s
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