If both the marker and the explicit respect of likeness are omitted, the resemblance is asserted with particular force. This is conventionally called tashbīh balīgh when the expression genuinely functions as a simile.
«زَيْدٌ أَسَدٌ»
Zayd is a lion.
With both terms present, the interpretation is that Zayd resembles a lion in courage so closely that the comparison is rhetorically presented as identity. This is not literal zoological identity. A different structure in which one term replaces another with a contextual clue leads into the discussion of metaphor (istiʿārah).