While the Gemara makes a number of suggestions regarding what the danger might be that lurks in holes between houses, what concerns the Gemara is how this fits with Rabbi Elazar’s teaching sheluhei mitzvah einum nizokim – that people involved in performing commandments are protected from danger.
Rav Ashi suggests that we may be concerned that aside from searching for hametz, perhaps the person will also turn his attention to find other missing objects during the search, and will not be actively involved in the mitzva at all times. The Gemara responds to this by arguing that even someone who has outside intentions beyond performing a mitzva will be credited for the mitzva if it is done. An example of this is taught in a baraita that rules that someone who gives charity and states that he is giving it in the hope that he will gain a share in the World-to-Come or that his sick child will recover is, nevertheless, considered a tzaddik gamur – a completely righteous person. The Gemara concludes that the rule that people involved in performing commandments are protected from danger only applies when danger cannot be anticipated. In a situation that is clearly dangerous we cannot apply that rule.
With regard to the man who gives charity with the expectation that he will derive some personal benefit from it, who the baraita says is a tzaddik gamur, the Ran points out that he might be considered righteous, but he would not be considered a hassid – a pious person. Some say that the only case where we can ignore the intent of the person doing the mitzva will be in the case of charity, where the recipient derives benefit from the assistance even if the intention of the giver was wrong. The Aruk has a variant reading in the Gemara, according to which the baraita does not label the man a tzaddik gamur, rather it rules that the donation was tzeddaka gemura – full fledged charity, without any character judgment about the person who made the donation.