split one's sides
Also, laugh one's head off. Be extremely amused, laugh uproariously. For example, That comedian had us splitting our sides, or Jane laughed her head off when she saw Rob's costume. The first of these hyperbolic terms dates from about 1700.
What Are Split Infinitives?Sometimes infinitives need a little space. A split infinitive occurs when there’s an adverb between two parts of an infinitive. An infinitive consists of the word to and the simple form of a verb (e.g. to go and to read). “To suddenly go” and “to quickly read” are examples of split infinitives because the adverbs (suddenly and quickly) split (or break up) the infinitives to …
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.