A bed which is used as a division in the midst of the house, and it (is) separate[s] - מטה החולקת בתוך הבית ומפסקת
According to רש"י the issue by a מטה המפסקת is whether בדיקה is required under the מטה. According to תוספות we are discussing a situation where the מטה divides the entire room into two sections. The inner side must be checked only if the bed is very high so one can walk underneath it without bending down or if it is sufficiently low that one can easily pass over the bed.
Here, it is where the dog can search after it - הכא כשהכלב יכול לחפש אחריו
If there is ודאי חמץ in a place where הכלב יכול לחפש אחריו; there is an obligation to remove it (even if there is a סכנת עקרב) by hiring workers. However if we are not sure if there is חמץ in a place where there is a סכנת עקרב, there is no obligation to search for חמץ.