I can never resist the temptation to try to explain maths!

Draw a circle to represent spring flowers (snowdrops, daffodils, winter flowering cherry, violets etc). Draw another circle, overlapping the first, to represent bulbs. The area which is inside both circles will contain this like snowdrops and daffodils - spring flowering bulbs. The rest of the second circle will have bulbs like leucojum which don't flower in the spring. The rest of the first circle will have violets and other spring flowers which aren't bulbs. The outside will have flowers which are neither spring flowering nor bulbs.

Or you could draw two circles, one inside the other, to represent "All cacti are succulents, but not all succulents are cacti".

They're useful to help visualise more complicated relationships than I've described, and usually with more than two circles needed. They were university stuff wen I was taught maths, but my children did them in primary school.