As a rule, all breeds of Orcs and Goblins expect the smaller greenskins to run away and it doesn't really alarm them when they do. The sight of fleeing or destroyed little 'uns simply reminds the bigger and bolder members of the horde why they are best - a mentality that has even spread to Trolls and Giants. To represent this:
Goblins do not take Panic tests caused by Snotlings.
Orcs (and war machines crewed by an Orc Bully) do not take Panic tests caused by Snotlings, Squigs or Goblins (including chariots and war machines crewed by Snotlings or Goblins).
Black Orcs do not take Panic tests caused by Snotlings, Squigs, Goblins or Orcs (including chariots and war machines).
Trolls only take Panic tests caused by other Trolls and Giants.
Giants only take Panic tests caused by other Giants.