Don't worry! This egg isn't on fire.
Pekkin never fail to deliver safe, spooky fun. Despite their somewhat creepy appearance, it's actually very difficult for them to surprise people as their body and tail emit a flame, which identifies them easily in the dark. Secondly, the green gas that Pekkins create also stays around for a while. So if a Pekkin "gets into position" to surprise you from around the corner, you'll probably see the green gas before you see them.
Pekkin gas has been extensively researched by the Science and Research Center in Ark City to ensure that it's not dangerous to humans. Because it's not, Pekkins are allowed to enter indoor spaces.