Telling the difference between native and Spanish bluebells.
The quickest way to start is to look at how the bells are growing: if they are all on the same side of the stem they are native; if they are all round the stem then they are Spanish. Once you get the knack it is easy. Then you notice that being one-sided the natives bend over a bit ("nodding bluebells"} , whereas the Spanish stand as straight as guardsmen; then you see the natives are much more delicate than the Spanish; then you see the native bells are long narrow tubes, whereas the Spanish are more open cups; and finally you see the natives are a lighter blue than the Spanish. Finally you wonder how you ever got them muddled in the first place.
Well, that was my experience anyway.