ותֵּרֶא שָׂרָה אֶת-בֶּן-הָגָר הַמִּצְרִית, אֲשֶׁר-יָלְדָה לְאַבְרָהָם--מְצַחֵק.
and she saw (Sarah) the son of Hagar the Egyptian, who had borne to Abraham מְצַחֵק
This word: מְצַחֵק m'tsah-KHAQ, has the same shoresh (root) as laugh, but here is used as a "mockery". Some translations say: "making sport". When it gets really interesting: as I looked for other uses of this word, מְצַחֵק, I found it in B'reisheet 26:8 when describing the action of Isaac on his wife, Rebecca (רבקה, or Rivka)
יִצְחָק מְצַחֵק, אֵת, רִבְקָה אִשְׁתּוֹ
Isaac מְצַחֵק with Rivka, his wife
Here, it is usually translated "caressing" . Not necessarily the negative implication that מְצַחֵק has with Hagar's son toward Isaac. Here's another:
The word is also in B'reisheet 19:14 in the context of how Lot's sons-in-law treated Lot when he tried to warn them of the coming destruction of Sodom and Gomorrah.
וַיְהִי כִמְצַחֵק, בְּעֵינֵי חֲתָנָיו
And he was like מְצַחֵק in the eyes of his sons in law
Just wondering when laughing at others becomes mocking? Evidently, when the mem is added to the front. In Ancient Hebrew, the mem stood for chaos, as in the tumultuous water of the seas.
So there is some Hebrew to ruminate on for a bit.