Paddy has a terrible pain

Paddy went to the doctors and said "doctor I have this terrible pain up my bottom."

"Drop your trousers Paddy", said the Doc. as he peered into Paddy's nether regions.

"Good grief Paddy", said the Doc "There's a lettuce up there".

"Is it serious" asked Paddy.

"I don't know Paddy,

Spoiler:

its only the tip of the iceberg"

.