Some hang in the water, heads tilted up, as though caught on an invisible line.
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He, however, never crossed that invisible line that clearly justified an overt reaction.
Christianity Today
Somewhere between 3,500m and 4,500m we crossed an invisible line.
Times,Sunday Times
His mouth had carried him across an invisible line.
Times, Sunday Times
The new government has made academics aware of an invisible line.
Times, Sunday Times