Long story short, you and Horror were being stupid together and ya ended up stepping on a bear trap, and horror tripped and fell...on top if ya...and it's Axe cut ya both

So OBVIOUSLY, like the "smart" adults you are. You tell no one and try to fix yourself instead of telling Nightmare

Eventually Cross walks in to ask if Horror has see his Capybara, and Saw you, A star sans (who's not even supposed to be here) and Horror, both bleed a ton. So obviously he helped y'all