Word splicing, or its more common name Sentence Mixing is a popular technique used in various YouTube Poops. In brief, it consists of editing clips of characters talking to make it sound like they are saying something else.
Sentence mixing splits off into two different levels, Sentences and Words. The latter is significantly more difficult to execute with accuracy.
Sentence mixing is most easily made by taking actual clips of a character saying something and rearranging them (example- "Mah Boi", "Dinner" "This Peace is what all true warriors strive for", take out the "peace", put "Dinner" in its place, and the king says "Mah Boi, this Dinner is what all true warriors strive for).
However, most of the time it is found that the characters do not say certain things the creator of the YTP wants them to say, such as swear words for example. In this case, it is required to take certain parts of something a character says, be it the beginning or end of a sentence, and merge them together (example- Link says "How about a kiss, for luck". Replace "l" in "luck" with "f" in "for" and Link says "Fuck"). Sometimes, you must even reverse that character's sound clips for the required phonemes.
Mixing more obscure sources into desired words requires a good ear, especially if it involves rearranging what a character's words are, rather than sentences.