Change one Letter

mug = pug...........

pug = hug..........

hug = bug......

Bug = Gun...............

gun=sun as in sunshine

sun = pun as in 'their once was a ...from...'

pun = run and here i go.......

Run = Rum.......with coke of course..

Rum = Sum....

sum = mum everyone has one

Mum = Gum...Wrigley's anyone..

gum = gym workout anyone

Gym = Slim....

Gym=Slim does not work???? slim is a 4 letter word?

So I will get us back on track GYM=GYP