Well. Angus is the world's greatest detective, so he definitely notices the weird skeleton with glowy eyes following him everywhere? But he's also not that concerned. He does remember Sans. Sans . . . helped a lot, back in Wonderland.

Which means that once Sans finally announces himself, Angus turns not with a smile but a look of Determination.

"Yes, sir! Would you like to hear one!!"

The second ! is audible.