Mettaton poking at Asriel's face gets the young boss monster to wrinkle his nose in response, and he instinctively pulls the warm covers closer towards him.

"Mm..."

Asriel does give a response, but instead of a snail fact, Mettaton gets...

"When does a skeleton laugh?" a few seconds pass before Asriel mumbles, "when something... tickles his funny bone..."