I have a theory. I had already noticed on 1-7 that the easter egg seemed to happen when the bottom right bird jumped in place and popped. The same thing happens with the big pig in 1-18. It also happens when it jumps in place then pops (the easter egg happens when it pops) and it's much easier to get due to the structure of the level. So far it happens with big pig wearing hats, but I'm not sure this is relevant. It's pretty clear now this was intentional. If I'm right, this would mean there's a sort of hidden bomb pig that could pop everything if hit right... Or something of the sort. Please tell me if you observe the same things and/or find any useful application elsewhere