Modelling balloons can be great fun at parties, but not everyone can transform a single balloon into a perfect scale replica of the Eiffel Tower or a recognisable giraffe. In fact very often people's attempt at a giraffe looks like a poodle and their poodles look like giraffes. A quick tip here - always do a Rolf Harris.
In other words, start making the model, asking them if they can 'guess what it is yet'. Once someone announces joyfully that they think they know what it is, agree with them, congratulate them and go with it - it's a lot simpler than trying to justify why your bison looks like a shih tzu. But in fact you don't have to always use modelling balloons for modelling. In fact they can be great fun for party games. For example, Inflate three balloons, and get six people to stand in a circle, facing outwards.
Then place all three balloons in the middle, and instruct everyone to reach between their legs and hold one end of any balloon in one hand, and one end of a different balloon in the other. Now the fun starts! They have to somehow turn themselves around so that they are all facing inwards, without letting go of the balloons at any time! It's a little like one of those infuriating Chinese puzzles, but with arms, legs and other parts not normally reached! The stretchy balloons are perfect for this sort of game, and can easily cope with the stretching, twisting and pulling, whereas normal balloons would just burst.