For a long while theories of flight and gravity meant that bees couldn't fly. Science is based on observation explanation and often requires repeated observations. As a result theories are only based upon a limited set of data that we have; furthermore many times they do not always appear to work in all situations or the conditions change which results in the theory having to adapt. As such it is possible for theories to have areas where they don't work or limitations upon them. Anti-science people capitalize upon this because they (more so than scientists) like to spread the belief that theories are perfect working understandings that are not capable of being wrong - that science knows everything and THIS is the theory. They then poke holes in it to disprove the stance and to show that science doesn't know everything. They tend to then harp on that the Bible knows everything there is to know. This is further aided by the fact that they will only ever get to basic school level theories. They will use those simplified school models to poke holes in, whilst only off-hand mentioning anything more advanced. The key here is that they know most of the audience will have been through a school system thus they can poke holes in that and the audience understands it. They leave the higher level stuff alone for specifics and only generally poke holes at that.