Two skeleton brothers are talking.
1st bro: "Hey, get up! You and do some exercise! You are so heavy, you weigh a ton!"
2nd bro: "A skele-TON :)"
The joke is a pun using the word 'skeleton' and 'a ton', a unit of weight. The second skeleton brother plays on the phrase to make it 'a skele-ton' as a play on words.
Dunno
Is this an UnderTale reference?
Papyrus
SANS!!!!