I read on CourtTV.com that the jury wanted the "self defense" definition and instructions for same to be reiterated to them. From Courttv.com:
In Massachusetts, homicide by reason of self-defense is justifiable, but it must meet three elements. First, jurors must consider Pring-Wilson's mental state. They need to consider whether he reasonably believed he was in imminent danger of suffering serious bodily harm or death, and that the only way to save himself was to use his knife.
He also must have exhausted any "reasonable alternative means of escape." The judge pointed out that "this rule does not impose an absolute duty to retreat," meaning that, in the 70 seconds — according to cellphone records — the men's paths crossed, Pring-Wilson may not have believed that he could run or walk away to escape.
The final element to justify self-defense is that the defendant must have used "no more force than is necessary to defend himself." This factor may be the biggest challenge for jurors to agree on, given the force necessary to puncture the victim's right ventricle. However, according to witness testimony, no one, not even the victim, was aware at first that Colono had been fatally stabbed.
If jurors have any reasonable doubt about whether Pring-Wilson acted in self-defense, they must choose acquittal. Prosecutors must prove beyond a reasonable doubt that at least one of the three elements needed for self-defense is absent.
The jury may be trying to rule out self defense to get that out of the way before they try to agree on the "degree" of the offense.