What did Tom and Huck do to take an oath not to reveal what they? Why did they do it? Chapter 10

Once they gain their breath, the boys rationalize as to what they should do. Not knowing that Injun Joe is attempting to frame Muff Potter for the murder, the boys decide to not tell a soul about what they had seen for fear that Injun Joe would seek revenge upon them as well. They sign a contract to keep their secret "mum" (an image of the contract in Tom's handwriting is placed within the text) and sign their initials in blood after pricking their fingers with needles. After they bury the contract, Huck and Tom hear a dog howling ­ a sign that death is coming, according to black slaves' tales.

when the boys saw injun joe murder he tried to blame muff potter for killing Dr Robinson. the boys were hiding behind a tree and watched everything. they were afraid that if they tell anyone injun joe will come for them.so they took an oath by writing on the tree with robinsonsblood