וַיֹּאכַל הָעָם עַל הַדָּם
(לב) וַיַּעַשׂ \{וַיַּעַט\} הָעָם אֶל ַשָּׁלָל \{הַשָּׁלָל\} וַיִּקְחוּ צֹאן וּבָקָר וּבְנֵי בָקָר וַיִּשְׁחֲטוּ אָרְצָה וַיֹּאכַל הָעָם עַל הַדָּם:
(לג) וַיַּגִּידוּ לְשָׁאוּל לֵאמֹר הִנֵּה הָעָם חֹטִאים לַיהֹוָה לֶאֱכֹל עַל הַדָּם וַיֹּאמֶר בְּגַדְתֶּם גֹּלּוּ אֵלַי הַיּוֹם אֶבֶן גְּדוֹלָה:
In this perek we are told that the Jews sinned by eating meat with blood. While the are a number of explanations as to what this means exactly, the simple meaning is that after fighting and fasting all day the Jews were so hungry and in a rush to eat that after they slaughtered their animals, they did not remove the blood properly before eating it.
One of the laws of making meat or chicken kosher is that after slaughtering the meat or chicken must be soaked and salted to remove the blood from the animal. In Hebrew this is known as מליחה. The videos below give a general overview of how chicken and meat is made kosher.
The Life of a Kosher Chicken