Since units have 100 hit points but the display only has one decimal place a unit that is still alive occasionally has it's strength rounded to zero. It is in practice on 0.05 or lower, (in effect 5 or less hit points out of 100) but it isn't displayed. This generally only occurs for scouts due to their very low starting strength. For stronger units 1% of their total strength is always more than 0.1, so this doesn't happen. I think one of the pictures in the funny screenshots thread also shows this.
