Their magical mishap is still in effect - the spell for summoning a daemon twisted, a little, and left them in each others' bodies. And, as they're still under the influence of alcohol and magical weed, they're afraid to dismiss Sistina and risk dismissing Papyrus, somehow, instead.

So it's the goose that first bounces over, wings fluttering in watchful excitement, to examine the cracked area... and loudly report on their findings. "The egg...? A foot!!"

And the skeleton that follows, nervously rubbing hands together, and asks everyone, "isn't this too fast? Did we mess something up?"