Crossed wires

At 2 o'clock this morning our phone started to ring a continuous and very loud ring. Dressing gown on and down stairs. When I lifted up the phone I got a dialing tone. When I put down the phone the continuous ring again. I cursed, unplugged it and went to bed.
This morning when I plugged it back in, the same continuous ring. But when I plugged in an old phone it was fine!!!
Wierd, until I looked at the bottom of the phone, where a slug had climbed into a hole and slimmed all over the inside.