בראשית כד,לג: וַיֻּישָׂם לְּפָּנָּיו לֶאֱכֹל וַיֹאמֶר לֹא אֹכַל עַד אִם־דִבַרְּ תִי דְּבָּרָּי וַיֹאמֶר דַבֵּר:
Playing on the word "va'Yusam", which, when spelt with a 'Samech' has connotations of poison. The Baal haTurim explains that they placed poison in his food (so that he should die, and they would then take all the money that he brought with him per Da'as Zekeinim) and then quickly sat down to eat so that he should not notice.
The only other time the word "va'Yusam" appears in the Torah is at the end of Sefer Bereshis (in connection with Yosef), where the Torah writes "va'Yusam bo'Oron be'Mitzrayim", a hint that they wanted to kill Eliezer and place his body in a coffin.
But he did notice, and when he said "I will not eat until ... ", adding "I am the servant of Avrohom", he meant that, as a servant of Avrohom, he was not used to eating before reciting the Berachos of 'al netilas yadayim' and 'hamotzi Lechem min haaretz'. He hoped that the Kos shel Berachah would work in his favor, and his faith was well-founded; an angel came and switched his plate with that of Besuel, who ate the poison and died.
