Many Glider constructions leave behind extraneous objects that need to be eliminated. In the lists of Glider constructions, these elimination reactions are not always shown, because most of these can be easily removed with a single Glider in a variety of ways.
One exception is in cases where a single Glider can be used to remove several objects at once, in which case it is shown as part of the reaction. Another case involves the Pond [8.7]. It has only one reaction, and that reaction takes 23 generations and a lot of space to finish, so it's not unsual that it might interfere with other objects. An easy way is to convert it to a Ship [6.2] and then easily eliminate that object with the [R7] reaction.