The kid running from this dog looks terrified. You'd think it's because the dog is dressed up like a lion. That makes sense, right? Let's have our dog dress up as a lion and scare people. The people will run for their lives because they think a lion is chasing them. Nope. The people are running because a huge dog is chasing them. The fact that it looks like a lion is secondary.
It reminds me of this prank where people dressed a small dog up like a giant spider. The costume had moving legs and everything. Needless to say, it was a terrifying prank. Think about people who are actually terrified of dogs though. If you did that prank on that person, they'd be scared either way. First at the spider, next at the dog.